Abstract: One of the most common secondary resistance mechanisms to ibrutinib (IBR, a first-generation, irreversible Bruton's tyrosine kinase [BTK] inhibitor) in CLL is the development of mutations in BTK involving Cys481, leading to impaired drug binding (Woyach et al, NEJM 2014; Furman et al, NEJM 2014). The mechanisms of resistance to second generation BTK inhibitors are currently unknown. We aimed to assess the spectrum of acquired BTK mutations in patients with CLL progression on zanubrutinib (ZANU), a second-generation, irreversible inhibitor of BTK. We identified 38 CLL patients, treated with ZANU on clinical trials (NCT02343120, NCT02569476, NCT03336333, NCT02795182) at three centres, for whom serial samples were available. Four of 38 patients (10.5%) had CLL progression on ZANU (time to progression 5, 26, 29 and 48 months) and underwent amplicon next generation sequencing (NGS) of BTK (exon 11, 15, 16) and PLCG2 (exon 16, 19-20, 24, 27-28). Remarkably, we detected a BTK kinase domain mutation, BTK Leu528Trp (NM_000061.2:c.1583T & gt;G), in all four patients progressing on ZANU. In addition, all four patients had detectable Cys481 mutations at lower variant allele frequency (VAF) than the BTK Leu528Trp (median BTK Leu528Trp 34.9% vs BTK Cys481 9.1%). Analysis of sequence reads from amplicon NGS and RNA-sequencing data demonstrated that BTK Leu528Trp and BTK Cys481 mutations were present on different alleles. Assessment of the BTK Leu528Trp and BTK Cys481 mutations with high sensitivity droplet digital PCR (ddPCR) confirmed the absence of both mutations prior to ZANU exposure in all patients (sensitivity 0.1% VAF). Longitudinal analysis of the four patients with the BTK Leu528Trp mutation demonstrated the appearance of the Leu528Trp coincident with rising measurable disease and subsequent clinical CLL progression. We then went on to test patients on ZANU without disease progression but with persistent measurable disease (n=34) by ddPCR and detected three further patients harbouring low level BTK Leu528Trp mutations (VAF & lt;1%). These mutations were first detected after a median of 40 months on ZANU therapy. The BTK Leu528Trp mutation has been described only once previously in a patient in the context of IBR resistance (who transformed with Richter's syndrome) where it co-occurred with Cys481 mutations (Maddocks et al, JAMA Oncol 2015). As the prevalence of BTK Leu528Trp among progressive disease samples in our cohort exceeds all prior reports in IBR-treated patients, we sought to further understand the specificity of BTK Leu528Trp for ZANU progression. Targeted sequencing in a cohort of 49 patients progressing on IBR from the European Research Initiative on CLL (ERIC) did not detect the BTK Leu528Trp in any patients (sensitivity 1% VAF). We went on to perform biochemical and cellular studies on the BTK Leu528Trp mutation. Assessment of enzymatic activity of BTKLeu528Trp demonstrated a significant loss of activity compared to both BTKWT and BTKCys481Ser. This was further confirmed by assessing BTK autophosphorylation in HEK293 cells. Autophosphorylation at BTK Tyr223 was markedly reduced in HEK293 cells stably expressing BTKLeu528Trp compared to both BTKCys481Ser and BTKWT. In addition, a crystal structure of apo-BTKLeu528Trp was solved to understand effects of BTKLeu528Trp on ZANU binding to BTK. The alignment of the crystal structure of apo-BTKLeu528Trp with that of BTKWT-ZANU or the modeled structure of BTK-ATP suggested potential steric clashes between BTKLeu528Trp and ZANU (Figure 1A), as well as BTKLeu528Trp and ATP (Figure 1B). In conclusion, we have described the novel enrichment of BTK Leu528Trp mutations occurring in patients with CLL progressing on ZANU and both structural and experimental data consistent with this mutation resulting in interference with both ATP and ZANU binding to BTK. These findings emphasize the potential for agent-specific resistance mutations with second generation BTK inhibitors and the need to include these mutations in diagnostic screening for BTK resistance in the clinic. SH/CPST co-first authors, CT/PB co-senior authors Disclosures Handunnetti: Abbvie: Other: Travel Grant; Gilead: Honoraria. Zhou:Beigene: Employment. Sun:Beigene: Employment. Xing:Beigene: Employment. Zhang:Beigene: Employment. Guo:Beigene: Employment. Sutton:Abbvie: Honoraria; Gilead: Honoraria; Janssen: Honoraria. Ghia:Dynamo: Consultancy, Honoraria; ArQule: Consultancy, Honoraria; BeiGene: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Research Funding; AbbVie: Consultancy, Honoraria, Research Funding; Gilead: Consultancy, Honoraria, Research Funding; Sunesis: Consultancy, Honoraria, Research Funding; Acerta/AstraZeneca: Consultancy, Honoraria; Pharmacyclics LLC, an AbbVie Company: Consultancy; Novartis: Research Funding; Juno/Celgene: Consultancy, Honoraria. Scarfo:AstraZeneca: Honoraria; Janssen: Honoraria; AbbVie: Honoraria. Seymour:Takeda: Consultancy; Acerta: Consultancy; Celgene: Consultancy, Research Funding, Speakers Bureau; AbbVie: Consultancy, Honoraria, Research Funding, Speakers Bureau; Janssen: Consultancy, Research Funding; Roche: Consultancy, Research Funding, Speakers Bureau. Anderson:Walter and Eliza Hall Institute: Employment, Patents & Royalties: Institute receives royalties for venetoclax, and I receive a fraction of these.. Roberts:AbbVie: Other: Unremunerated speaker for AbbVie, Research Funding; Australasian Leukaemia and Lymphoma Group: Membership on an entity's Board of Directors or advisory committees; Walter and Eliza Hall Institute: Patents & Royalties: Institute receives royalties for venetoclax, and I receive a fraction of these.; Janssen: Research Funding; BeiGene: Research Funding. Huang:Genentech: Patents & Royalties: DCSH is an employee of the Walter and Eliza Hall Institute which receives milestone and royalty payments related to venetoclax. Liu:Beigene: Employment. Cheah:Roche, Janssen, MSD, Gilead, Loxo Oncology, Acerta, BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene, Roche, Abbvie: Research Funding; Roche: Other: Travel expenses. Tam:Janssen: Honoraria, Research Funding; BeiGene: Honoraria; Pharmacyclics LLC, an AbbVie company: Honoraria; Roche: Honoraria; Novartis: Honoraria; AbbVie: Honoraria, Research Funding. Blombery:Janssen: Honoraria; Invivoscribe: Honoraria; Novartis: Consultancy.

Abstract: The BCL2 Gly101Val mutation may be acquired in patients with chronic lymphocytic leukaemia (CLL) treated with venetoclax (VEN), leading to reduced drug binding affinity and secondary resistance. In the majority of patients, the Gly101Val mutation is subclonal within the CLL compartment consistent with the presence of alternative resistance mechanisms in CLL cells not harboring the Gly101Val mutation. To date, two Gly101Val mutated patients have been identified with co-existing candidate resistance mechanisms in Gly101Val non-mutated cells; one with BCL-XL over-expression (Blombery et al, Cancer Discov., 2019) and another with a second subclonal candidate BCL2 resistance mutation - Asp103Tyr (Tausch et al, Haematologica 2019). Given the possibility of additional resistance mechanisms, we investigated patients with progressive CLL on VEN harboring the Gly101Val mutation for the presence of additional acquired resistance mutations in BCL2. Ten patients with progressive CLL on VEN with Gly101Val mutations were identified by sensitive allele-specific droplet digital PCR. To further assess for alternative BCL2 mutations in this cohort we performed ultra-deep amplicon-based next generation sequencing (NGS) (median depth ~50,000X) targeting BCL2. An amplicon variant caller (Canary) specifically designed for low level variant calling was used (Doig et al, BMC Bioinformatics, 2017). To achieve enhanced specificity we performed digital NGS with PCR error-correction using unique molecular indexes (UMI) (QiaSEQ Targeted DNA Panel). Given the high GC content of BCL2 we also used hybridization-based NGS using a custom targeted panel (Blombery et al, BJH 2017) combined with a sensitive unpaired variant caller (GATK4/Mutect2). In 7/10 (70%) patients, BCL2 mutations in addition to the Gly101Val were detected. Recurrent mutations (detected in more than one patient) were Asp103Tyr, Asp103Glu, Arg107_Arg110dup, and Val156Asp. All additional recurrent mutations were confirmed to be absent prior to commencing VEN (sensitivity 1% variant allele frequency[VAF]). Phase-analysis of NGS reads was consistent with the presence of the additional recurrent mutations on different alleles (and therefore cells, assuming heterozygosity) to both each other and to Gly101Val. Multiple addition recurrent mutations were observed in patients in the cohort with one patient harboring three recurrent mutations in addition to the Gly101Val (Asp103Tyr, Asp103Glu, Val156Asp). In multiple patients in the cohort, the VAF of non-Gly101Val mutations exceeded that of the Gly101Val mutation. Importantly, in all patients a significant (albeit variable) proportion of CLL cells were found to be BCL2 wild-type consistent with the presence of as yet unidentified resistance mechanisms unrelated to BCL2 mutations. In one patient, two additional non-recurrent mutations were observed (Ala113Gly and Arg129Leu) in addition to Gly101Val and Val156Asp. Again, all four mutations in this patient were observed to be in mutually exclusive NGS reads. Strikingly, all of the recurrent acquired BCL2 mutated residues identified in our cohort are situated in the BCL2 binding groove that binds VEN (Figure 1). The Asp103 codon in the P4 pocket is critical for VEN binding through hydrogen bonding between its sidechain and the azaindole moiety of VEN. The Asp103Glu mutation is noteworthy given that the equivalent residue to Asp103 in BCL-XL is a Glu, which reduces VEN binding to BCL-XL. The Val156 mutation situated at the base of the P2 pocket is close to the chlorophenyl moiety of VEN and a change to Asp in this position may disrupt VEN binding. Ongoing binding experiments and modeling in cellular systems will further elucidate the mechanism and contributions of these new recurrent mutations to VEN resistance. In summary, we have extended the landscape of acquired candidate resistance mutations occurring in patients treated with VEN to include four novel recurrent BCL2 mutations. Moreover, our data are consistent with the emerging observation of multiple acquired resistance mechanisms operating in different CLL cells in a single patient contributing to an "oligoclonal" pattern of clinical relapse on VEN therapy. Figure 1 - BCL2 protein structure surface bound to venetoclax (VEN) in orange. The Asp103Tyr, Asp103Glu and Val156Asp mutation sites are shown in red and Arg107_Arg110dup region in blue Disclosures Blombery: Janssen: Honoraria; Invivoscribe: Honoraria; Novartis: Consultancy. Anderson:Walter and Eliza Hall Institute: Employment, Patents & Royalties: Institute receives royalties for venetoclax, and I receive a fraction of these.. Seymour:Acerta: Consultancy; Celgene: Consultancy, Research Funding, Speakers Bureau; Janssen: Consultancy, Research Funding; AbbVie: Consultancy, Honoraria, Research Funding, Speakers Bureau; Roche: Consultancy, Research Funding, Speakers Bureau; Takeda: Consultancy. Huang:Genentech: Patents & Royalties: DCSH is an employee of the Walter and Eliza Hall Institute which receives milestone and royalty payments related to venetoclax. Roberts:AbbVie: Other: Unremunerated speaker for AbbVie, Research Funding; Australasian Leukaemia and Lymphoma Group: Membership on an entity's Board of Directors or advisory committees; Janssen: Research Funding; Walter and Eliza Hall Institute: Patents & Royalties: Institute receives royalties for venetoclax, and I receive a fraction of these.; BeiGene: Research Funding.

Abstract: Background: Marginal zone lymphoma (MZL) is an incurable but heterogeneous disorder for which there is no standard of care treatment in the relapsed/refractory (R/R) setting. The BTK inhibitor, ibrutinib (IB) is well tolerated with an overall response rate (ORR) of 48% as monotherapy in R/R MZL but rarely complete remission (Noy et al, Blood, 2017). The BCL-2 inhibitor, venetoclax (VEN) has also been evaluated in a small number of R/R MZL patients (pts) with evidence of activity and tolerability (Davids et al, JCO, 2017). We sought to evaluate the efficacy and safety of combination IB and VEN in pts with MZL based upon the rationale of (1) distinct mechanisms of action, (2) activity as monotherapies in MZL, and (3) acceptable non-overlapping toxicity profiles. We report preliminary results of the MZL cohort of an investigator-initiated phase II trial of combination IB and Ven (NCT02471391). Methods: Pts with MZL by WHO 2008 criteria who were R/R or treatment naïve but considered inappropriate for treatment with chemotherapy were enrolled. Pts commenced treatment with IB monotherapy at a dose of 560mg per day. After 4 weeks, VEN was added to IB treatment, in weekly step-wise dose escalation over 6 weeks to a target dose of 800mg per day in the initial cohort (n = 4), amended to 400mg per day, due to a reported IB-VEN drug interaction in a similar trial (NCT02910583). The primary endpoint was the complete remission rate (CRR) at 16 weeks. The secondary endpoints were to determine ORR and CRR, to determine minimal residual disease (MRD) elimination rates, to describe progression free survival (PFS), overall survival, duration of response, time to progression and frequency and severity of adverse events. Investigator-assessed response assessments, based on IWG criteria (Cheson et al, JCO, 2007), were performed with CT at 4, 16, 28, 40 and 56 weeks, PET/CT at weeks 16 and 56, and bone marrow (BM) aspirate and trephine, and MRD assessments by flow cytometry at all time-points. Results: Fourteen of 15 planned pts were enrolled at the time of data cut-off (May 2019), of whom 12 had reached the week 16 primary endpoint or discontinued and are reported here. Two remain on study for 〈 16 weeks at data cut-off. The median age was 68 years (range, 39 - 80yrs). Baseline characteristics are shown in Table 1. Seven pts (58%) had R/R MZL with median 1 prior therapy; 5 (42%) were treatment naïve. All pts received treatment, completing IB monotherapy and commencing the VEN and IB combination. One pt discontinued treatment during VEN escalation (50mg Ven) due to grade 4 drug-induced hepatitis, attributed to IB following rechallenge. The median follow-up is 9.7 months (range, 3-12 months). The CRR with CT assessment at week 16 was 25% (3/12). The CRR including PET assessment was 42% (5/12) at week 16. The ORR at this time-point was 58% (7/12) by CT and 84% (10/12) by PET (historical control with IB monotherapy is 3%; Noy et al, Blood, 2017). MRD clearance (10^-4 sensitivity) in BM was confirmed in 1 of 7 evaluable pts. Two pts have developed PD after 7 and 11 months of treatment commencement. No deaths have occurred. Safety analysis shows no cases of tumour lysis syndrome, and only one (8%) discontinuation due to toxicity. Grade 1-2 atrial fibrillation (AF) occurred in 2 pts (17%), suspected to be related to IB. The most common non-hematologic toxicities were diarrhea, bruising, fatigue and nausea, and were largely low grade. The most common hematologic toxicities were neutropenia (n=6) and thrombocytopenia (n=5) including grade 3-4 events (2 and 1 events, respectively). Serious adverse events (SAE) occurred in 5 subjects (1 pt had 2 SAE's), including 2 events attributable to trial therapy. Overall 2 pts (17%) required permanent dose reduction of IB to 420mg, due to grade 2 AF and due to grade 3 febrile illness in these cases. One pt (8%) required permanent dose reduction of VEN to 300mg, due to grade 4 neutropenia lasting 〉 7 days despite use of G-CSF. Conclusions: Combination IB and VEN is a promising safe and efficacious treatment for MZL. Our preliminary data, demonstrating high response rates including frequent CR, warrants further investigation in a larger study. Disclosures Handunnetti: Gilead: Honoraria; Abbvie: Other: Travel Grant. Khot:Amgen: Speakers Bureau; Kyowa Hakko Kirin: Consultancy; Janssen: Consultancy; Amgen: Consultancy; Celgene: Consultancy. Anderson:Walter and Eliza Hall Institute: Employment, Patents & Royalties: Institute receives royalties for venetoclax, and I receive a fraction of these.. Blombery:Novartis: Consultancy; Janssen: Honoraria; Invivoscribe: Honoraria. Ritchie:Sanofi: Honoraria; Novartis: Honoraria; Imago: Research Funding; Beigene: Research Funding; Takeda: Research Funding; Amgen: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy; BMS: Research Funding. Hicks:Telix Pharmaceuticals: Equity Ownership; Ipsen: Research Funding; Clarity: Research Funding. Bressel:Regeneron Pharmaceuticals: Consultancy. Roberts:Australasian Leukaemia and Lymphoma Group: Membership on an entity's Board of Directors or advisory committees; Walter and Eliza Hall Institute: Patents & Royalties: Institute receives royalties for venetoclax, and I receive a fraction of these.; AbbVie: Other: Unremunerated speaker for AbbVie, Research Funding; Janssen: Research Funding; BeiGene: Research Funding. Seymour:Janssen: Consultancy, Research Funding; AbbVie: Consultancy, Honoraria, Research Funding, Speakers Bureau; Takeda: Consultancy; Acerta: Consultancy; Roche: Consultancy, Research Funding, Speakers Bureau; Celgene: Consultancy, Research Funding, Speakers Bureau. Tam:Novartis: Honoraria; Janssen: Honoraria, Research Funding; AbbVie: Honoraria, Research Funding; BeiGene: Honoraria; Roche: Honoraria; Pharmacyclics LLC, an AbbVie company: Honoraria. OffLabel Disclosure: Discussion of off-label use: Venetoclax and combination venetoclax and ibrutinib are not approved in the US for use in marginal zone lymphoma.

Abstract: Venetoclax induces high rates of response (~80%), including complete remissions (CR) in patients with heavily pre-treated chronic lymphocytic leukemia (CLL) through inhibition of BCL2. Despite achieving deep and durable responses, most patients will eventually experience disease progression on treatment. The molecular mechanisms that mediate clinical resistance to venetoclax in vivo are largely unknown. From a cohort of 67 relapsed CLL patients (Anderson et al, Blood 2017; 129:3362-3370) treated with venetoclax on three early phase clinical trials, we performed focussed genomic evaluation in those with CLL-type progressions (as opposed to large cell Richter's transformation). Targeted amplicon next generation sequencing of a panel of 33 genes recurrently mutated in lymphoid malignancy was performed where suitable pre- and post-progression samples were available. Twenty-one patients experienced CLL progression after a median of 36 months (range 6 - 73). Fifteen patients had paired samples for detailed analyses. A single heterozygous nucleotide variant was detected in BCL2 (NM_000633.2:c.302G 〉 T, p.(Gly101Val)) in progression samples in 7 of 15 patients (Fig 1A). Further investigation using a highly sensitive (limit of detection 0.01%) and specific droplet digital PCR (ddPCR) assay indicated that the Gly101Val mutation was first detected at low variant allele fraction after 19-42 months on venetoclax, up to 25 months earlier than when standard disease progression criteria were met. The Gly101Val was not detected prior to venetoclax treatment in this cohort and was not detected in a series of samples from patients treated at our institution who had not received venetoclax (CLL [n=74], NHL [n=198] , myeloma [n=103]) nor has it been described in cancer (COSMIC) or population (gnomAD) databases. To investigate whether Gly101Val directly causes resistance to venetoclax, we expressed it in two B-lineage cell lines (RS4;11 and KMS-PE-12). Gly101Val cells were ~30-fold less sensitive to venetoclax than cells expressing wild-type (WT) BCL2. The Gly101Val mutation conferred a selective advantage during continuous exposure to sublethal concentrations of venetoclax in 3-week cultures. The same phenomena was observed with primary patient Gly101Val mutant cells in both short-term survival assays and when cultured in a bone marrow stromal model (Thijssen et al, Haematologica 2015;100:302-6). On stroma, primary cells bearing the Gly101Val mutation demonstrated markedly increased resistance to venetoclax with concentrations higher than achievable clinically in vivo. In the absence of venetoclax, the Gly101Val mutant demonstrated preserved normal function by protecting cell lines from apoptosis induced by cytotoxics with similar effectiveness to WT BCL2. In binding assays, the capacity for venetoclax to compete in vitro with BIM for binding to the Gly101Val mutant was markedly reduced (~180-fold) compared to WT BCL2. This is most likely explained by the presence of a bulkier valine residue in a region juxtaposed to the venetoclax binding groove (Fig 1B). In cell-based assays, whilst venetoclax readily displaced BAX and BAK from WT BCL2 it was ineffective when these pro-apoptotic molecules were bound to the Gly101Val mutant. We observed that not all CLL cells at progression carried the Gly101Val mutation. One patient harbored distinct subclones with and without the BCL2 Gly101Val mutation at progression. The subclone with exclusively WT BCL2 was observed to have elevated BCL-xL by mass cytometry (CyTOF), while the Gly101Val clone had minimal BCL-xL expression. Together these data indicate that whilst the Gly101Val mutation is sufficient to enable clinical resistance to venetoclax, alternative mechanisms may also mediate resistance in the same patient. In conclusion, we have identified and functionally characterized a novel recurrent BCL2 mutation (Gly101Val) emerging in a cohort of patients with CLL-type progressions treated with venetoclax. The BCL2 Gly101Val impairs binding of venetoclax to BCL2, confers resistance to venetoclax in both patient leukemia cells and engineered cell lines, and provides a selective growth advantage over wild-type cells when maintained in the presence of the drug in vitro. This mutation provides new insights into the pathobiology of venetoclax resistance and provides a potential biomarker of impending clinical relapse. Figure 1 Figure 1. Disclosures Anderson: Walter and Eliza Hall: Employment, Patents & Royalties; AbbVie, Inc: Research Funding; Genentech: Research Funding. Gong:The Walter and Eliza Hall Institute of Medical Research: Other: Institutional funding for venetoclax including milestone and royalty payments.. Thijssen:The Walter and Eliza Hall Institute of Medical Research: Other: Institutional funding for venetoclax including milestone and royalty payments.. Birkinshaw:The Walter and Eliza Hall Institute of Medical Research: Other: Institutional funding for venetoclax including milestone and royalty payments.. Teh:The Walter and Eliza Hall Institute of Medical Research: Other: Institutional funding for venetoclax including milestone and royalty payments.. Xu:The Walter and Eliza Hall Institute of Medical Research: Other: Institutional funding for venetoclax including milestone and royalty payments.. Flensburg:The Walter and Eliza Hall Institute of Medical Research: Other: Institutional funding for venetoclax including milestone and royalty payments.. Lew:Walter and Eliza Hall: Employment, Patents & Royalties. Majewski:Abbvie: Patents & Royalties: I am an employee of the Walter and Eliza Hall Institute which receives milestone and royalty payments related to venetoclax. Gray:The Walter and Eliza Hall Institute of Medical Research: Other: Institutional funding for venetoclax including milestone and royalty payments.. Tam:Gilead: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Abbvie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; BeiGene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pharmacyclics: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria, Research Funding. Seymour:AbbVie: Consultancy, Honoraria, Research Funding; F. Hoffmann-La Roche Ltd: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Genentech Inc: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Honoraria, Research Funding; Celgene: Consultancy. Czabotar:The Walter and Eliza Hall Institute of Medical Research: Other: Institutional funding for venetoclax including milestone and royalty payments.. Huang:The Walter and Eliza Hall Institute of Medical Research: Other: Institutional funding for venetoclax including milestone and royalty payments.. Roberts:Walter and Eliza Hall: Employment, Patents & Royalties: Employee of Walter and Eliza Hall Institute of Medical Research which receives milestone and royalty payments related to venetoclax; AbbVie: Research Funding; Genentech: Research Funding; Janssen: Research Funding.

Abstract: CNS relapse is a devastating and usually fatal complication of NHL, and controversy exists regarding the best methods of CNS prophylaxis. We have previously shown that IT alone is inadequate in patients (pts) with aggressive NHL at high risk of CNS relapse (Leuk Lymphoma2002;43:1783). We therefore assessed the efficacy of adding systemic HD-MTX to IT prophylaxis, based on drug penetration into the CSF and brain parenchyma. Methods: from 1/91 to 3/08, 85 pts with newly diagnosed aggressive NHL and negative baseline CSF cytology were treated with CNS prophylaxis due to risk factors such as multiple extranodal (EN) sites and elevated LDH. Patients were classified into 3 groups: CHOP-like therapy & IT (n=24), systemic therapy incorporating HD-MTX (≥1g/m2 eg Hyper-CVAD; n=25) and CHOP-like therapy & IT followed by 2 doses of MTX 3g/m2 24 hour CIVI q14d (n=36). Results: Median age was 52 years (16–82). Groups 1, 2 and 3 were similar in proportions of advanced stage (III and IV), baseline LDH 〉 1× ULN, gender, performance status and number of extranodal sites. Groups 2 & 3, who both received HD-MTX, were similar and were combined for all analyses. The CNS risk index (van Besien Blood1998;91;1178) was well matched for group 1 versus Groups 2/3 combined (P=0.3). The median number of IT treatments received was 5 (1 – 6) in group 1 and 6 (1 – 13) in groups 2/3. HD-MTX administration (total 101 admissions) was safe with a median 4(1–27) days inpatient stay and no treatment-related mortality. Complications included reversible renal impairment and mucositis grade ≥2 in 4% and 2% of cycles respectively. With a median follow-up of 29.5 months (2.6–164.4) there are 8 CNS relapses; 6 in group 1, 0 in group 2 and 2 in group 3. Sites of CNS recurrence were leptomeningeal alone in 4, isolated parenchymal in 2 and both in 2. All CNS recurrences occurred within 25.5 months (range 3.7–25.5) from diagnosis. Median survival after CNS relapse was 118 (14–264) days. Pts receiving systemic HD-MTX had a lower rate of CNS recurrence compared to group 1 pts (At 30 Mo; 4.5 ± 3% versus 27 ± 10%; P = 0.0033; figure 1). The only predictor for CNS relapse was the absence of systemic HD-MTX, with a hazard ratio of 10.07 (95%CI 2.16–46.97) for relapse in the IT-alone group (P=0.003). The relative risk of CNS relapse was 0.13 (0.03-0.6) in the groups treated with IT plus systemic HD-MTX. The 5-year actuarial CNS-relapse free survival rates were 42 ± 11% for group 1, and 82 ± 7% for groups 2/3 (P=0.0003). Conclusion: These data demonstrate that IT alone is inadequate CNS prophylaxis in at-risk patients with aggressive NHL. The addition of systemic HD-MTX either as part of primary therapy or administered following CHOP-like therapy significantly reduces CNS recurrence and may improve overall survival. Figure SEQ Figure \* ARABIC 1: CNS relapse in patients receiving IT chemotherapy alone compared to IT plus IV HD-MTX Figure. SEQ Figure \* ARABIC 1: CNS relapse in patients receiving IT chemotherapy alone compared to IT plus IV HD-MTX

Abstract: Background: Myelodysplastic syndromes (MDS) are characterized by ineffective hematopoiesis leading to cytopenias, including anemia and thrombocytopenia. KER-050, a modified activin receptor type IIA inhibitor, is designed to target transforming growth factor-β ligands, including activin A. In preclinical studies, KER-050 promoted the maturation of progenitors across the full spectrum of erythropoiesis and thrombopoiesis and elicited bone anabolic effects. In a Phase 1 study in healthy participants, KER-050 treatment resulted in robust and sustained increases in reticulocytes (RETs), hemoglobin (HGB), and platelets. Increases in the bone formation marker bone specific alkaline phosphatase were also observed. Here we report results of an ongoing Phase 2 study to evaluate whether KER-050 provides therapeutic benefit in MDS patients with anemia. Aims: Evaluate safety, tolerability, pharmacodynamics and efficacy of ascending doses of KER-050 in participants with MDS in an open-label, 2-part Phase 2 study. Methods: IPSS-R very low-to-intermediate risk MDS patients (both RS+ and non-RS) with anemia (HGB & lt;10g/dL or requiring RBC transfusions) are enrolled. In Part 1, ascending dose cohorts receive KER-050 subcutaneously every 4 weeks for 4 doses starting at 0.75mg/kg until a recommended Part 2 dose is determined. Part 2 dose expansion will begin following Part 1, with treatment extended to 2 years. Safety endpoints include incidence of adverse events (AEs); erythroid efficacy endpoints (≥8 weeks duration) include rates of transfusion independence (TI) in transfused participants, reduction in RBC transfusions by ≥4 units or ≥50% reduction in high transfusion burden participants (HTB) and HGB increase ≥1.5g/dL in non-transfused (NT) and low transfusion burden (LTB) participants. Results are reported for efficacy-evaluable participants in cohorts 1 and 2 of Part 1 dose escalation, defined as having ≥8 weeks of HGB and transfusion data. Results: At data cut-off (July 10, 2021) with median follow-up of 140 days (range 1 to 169 days), 17 participants had received ≥1 dose of KER-050 across 3 dose levels: 0.75 mg/kg, 1.5 mg/kg and 2.5 mg/kg. Baseline characteristics are described in Table 1. No related serious AEs, dose-limiting toxicities, or dose modifications were reported. One participant developed grade 2 maculopapular rash after the first dose which was considered treatment related, resolved and did not recur with subsequent doses. No other related AEs were reported. Two discontinued study drug prior to end of treatment: 1 due to participant decision, 1 due to death unrelated to study drug. None developed high risk MDS or AML. In 10 efficacy-evaluable participants, overall erythroid response rate was 60% (n=6/10). 33% (n=1/3) NT participants had a HGB increase of ≥1.5g/dL sustained ≥ 8 weeks. 5 of 7 transfused participants (71%) (n=1/2 LTB and n=4/5 HTB; n=2/3 non-RS and n=3/4 RS+) had erythroid responses sustained ≥8 weeks (range 8-20 weeks, ongoing) and 57% (n=4/7) achieved TI (Figure 1, Panel A). Maximum increase from baseline in RETs observed in transfused responders (TR) (n=5) was 24.6 x10 9/L (mean), range 10.5- 41.6 x10 9/L from day 1-29 with increases in RETs seen after each dose (Panel B). Maximum reduction in serum ferritin in TR was 40.4% (mean), range 10-66%, and maximum increase in soluble transferrin receptor (sTfR) was 52.8% (mean), range 29.8-116.4%. Increases in platelets were observed in TR (Panel C). Mean baseline platelet count for TR was 234 x10 9/L (range 104-401 x10 9/L), and maximum increase from baseline was 130 x10 9/L (mean), range 32-235 x10 9/L. No participants required dose reduction due to thrombocytosis. Summary: Erythroid responses have been observed in RS+ and non-RS MDS patients including reduction in transfusion burden at the initial dose levels. Observed increases in RETs and sTfR and observed decreases in ferritin suggest that KER-050 treatment is potentially associated with increased erythropoiesis. Increases in platelets have been observed in TR. These data support the potential of KER-050 as a treatment for multilineage cytopenias in MDS by potentially targeting multiple stages of hematopoiesis. As of data cut-off, KER-050 has been well tolerated. Dose escalation is ongoing in this Phase 2 study of anemic patients with MDS; data from planned cohorts from Part 1 will be presented. Part 2 dose expansion phase is expected to initiate prior to the meeting. Figure 1 Figure 1. Disclosures Ross: Bristol Myers Squib: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Keros Therapeutics: Consultancy, Honoraria. Arbelaez: Amgen: Other: Travel, Accommodations, Expenses. Chee: Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees. Fong: AbbVie: Consultancy; Amgen: Consultancy; Astellas: Consultancy, Research Funding; Bristol Myers Squibb: Consultancy; Novartis: Consultancy, Speakers Bureau; Phizer: Consultancy; Novotech: Honoraria; Specialised Therapeutics: Honoraria. Hiwase: Novartis: Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees. Wight: Jannsen: Honoraria, Other: Travel subsidies; Abbvie: Honoraria, Other: Travel subsidies. Rovaldi: Keros Therapeutics: Current equity holder in publicly-traded company. Furutani: Keros Therapeutics: Current Employment, Current equity holder in publicly-traded company. Gaggi: Keros Therapeutics: Current Employment, Current equity holder in publicly-traded company. Jiang: Keros Therapeutics: Current Employment, Current holder of stock options in a privately-held company. Lachey: Keros Therapeutics: Current Employment, Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees. Natarajan: Keros Therapeutics: Current Employment, Current equity holder in publicly-traded company. Ordonez: Keros Therapeutics: Current Employment, Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees.

Abstract: Abstract 3187 Thromboembolism (TE) is an important complication of cancer with substantial clinical implications. MM, treated with thalidomide (thal) and LEN, has TE rates up to 25%, particularly when used in combination with chemotherapy and corticosteroids. Given disease heterogeneity, bleeding and TE risks are different for all patients and individuals over time. With the emergence of novel antithrombotic agents, further understanding of the pathophysiology of both MM- and therapy-related hemostatic dysfunction and the identification of important biomarkers, may promote a risk-stratification process and allow a targeted therapeutic strategy. We prospectively and sequentially assessed novel thrombogenic biomarkers, with a plan to correlate with functional assays (thrombin generation and microparticles) in R-MM, before and after exposure to LEN/dex as part of a 150-patient phase-II clinical trial. Hemostatic assessments were performed at enrolment, 1-, 4-, 12-months and/or end of study. 27 patients at our institution, 15 males, median age 69 years (range 58–80) were included in the analysis: 16 had IgG monoclonal protein (13 kappa [k]), 9 IgA (6 k), 2 were k light chain only. The karyotype was diploid in 18, complex in 4 and 3 patients had t(4;14), t(11;14) or t(8;14) respectively. Median number of prior lines of therapy was 3 (range 1–7); 18 had prior thal and 15 had received a melphalan-based autologous stem cell transplant. Median (range) for Hb was 111g/L (80-137) and creatinine clearance 66.6mL/min (23-182). 6/27 had a prior TE: 1 arterial, 5 venous. All patients commenced antithrombotic therapy at enrolment: 20 received aspirin (100mg/day), 4 prophylactic and 2 therapeutic dose enoxaparin, 1 treatment dose warfarin. At enrolment (pre-LEN/dex) and after 4 weeks of therapy, the median (range) for the individual assays are outlined in table 1. Pre-LEN/dex: FVIIIc, vWFAg, Fib Mon, TAT, PF1+2 and TM were markedly elevated in the majority of patients. After 4 weeks of therapy, many biomarkers remained elevated, however, Fib Mon and PMN-E near normalised in all patients; FVIIIC and vWFAg was elevated in less patients; while Fib, PF1+2 and TAT increased. This early promising data demonstrate inflammatory, endothelial and hemostatic dysregulation in R-MM with an altered biomarker profile after exposure to LEN/dex. Further results of sequential analyses will be presented at the meeting. Study (cycle, day) C1D1 (pre–LEN/dex) n* C2D1 (4–weeks LEN/dex) n* Biomarker (units, NR) Median Range 〉 ULN, 〈 LLN Median Range 〉 ULN 〈 LLN APTT (s, 24–34) 34 24–48 13 0 33 26–52 8 0 PT (s, 11.8–14.6) 13.5 12–25.6 10 0 13.2 11.2–45.2 2 3 Fib (g/L, 2.0–4.0) 4 2.4–6.8 12 0 5.5 0.7–8.4 21 2 D-dimer (mg/L, 0.0–0.5) 0.5 0.1-1.5 9 NA 0.6 0.1–6.4 15 NA Plt (×109/L, 150–450) 214 43–372 0 7 225 30–385 0 6 FVIIIc (%, 50–150) 298 96–600 22 0 236.5 159–600 10 0 vWFAg (%, 50–160) 206 98–325 18 0 298 148–364 12 0 APC-R ratio (2–3.5) 2.3 1.7–3.4 0 3 3.2 1.7–3.6 1 1 AT (%, 80–120) 98 69–135 3 3 108 77–126 4 1 Fib Mon (μg/ml, 0.1– 6) 4.3 2.0–61.2 8 0 3.1 0–95 2 1 TAT (μg/L, 〈 2.0–4.2) 1.1 0.4–37.6 9 14 8.1 2.7–54.7 19 0 PF1+2 (pmol/L, 69–229) 192.3 0.7–705.5 11 2 197.3 35.8–1266.5 8 5 anti-CG (U/ml, 〈 15) 0.2 0-5.2 0 NA 0.1 0–0.6 0 NA TM (pg/mL, 2353–4541) 4739.1 2628–11656.3 15 0 4050.3 244–10613.2 8 2 PMN-E (ng/mL, 0–90) 44 22–276 6 NA 34.8 14–92 1 NA NR: Normal range; APTT: Activated partial thromboplastin time; PT: Prothrombin time; Fib: Fibrinogen; Plt: Platelet count; FVIIIc: Factor VIII-coagulant; vWFAg: von Willebrand factor Antigen; APC-R: Activated protein C resistance ratio; AT: Antithrombin; Fib Mon: Fibrin Monomers; TAT: Thrombin-antithrombin complex; PF1+2: Prothrombin fragments1+2; CG: Cathepsin G; TM: Thrombomodulin; PMN-E: PMN Elastase; NA: values 〈 LLN or 〉 ULN not clinically applicable. * Number of patients (n) within the cohort (n=27), in whom measured level was 〉 upper limit of normal ( 〉 ULN) or 〈 lower limit of normal ( 〈 LLN). Disclosures: Curnow: Celgene: Research Funding; Novartis: Consultancy. Lynch:Celgene Pty Ltd: Employment, Equity Ownership. Harrison:Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Prince:Celegene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Westerman:Celgene: Research Funding.

Abstract: Venetoclax (Ven) is an effective element of treatments for chronic lymphocytic leukemia (CLL) with high response rates observed in the upfront and relapsed/refractory (R/R) settings. In addition to inducing apoptosis in CLL cells, Ven also induces apoptosis within normal and malignant myeloid lineage populations (accounting for its efficacy in the treatment of acute myeloid leukemia). We investigated the effects of Ven outside the target tumor compartment in patients (pts) with CLL receiving long-term continuous Ven and make the novel observation of the development of BAX-mutated clonal hematopoiesis in this heavily pre-treated patient group. 92 pts with CLL receiving continuous non time-limited Ven have been treated at our institutions on clinical trials. Of these, 41 had sufficient ( & gt;6 mo) follow up (median 70; range 14-95 mo) and suitable samples available for further analysis. 38/41 (93%) pts had received previous treatment with alkylators and/or fludarabine. In order to assess the non-CLL compartment in these 41 pts we identified those with peripheral blood or bone marrow aspirate samples taken during deep response to Ven demonstrating either minimal ( & lt;5%) or no CLL involvement by flow cytometry (sensitivity 10-4). We initially performed unique molecular index (UMI)-based targeted next generation sequencing of apoptosis pathway genes as well a panel of 60 genes recurrently mutated in lymphoid and myeloid malignancy. From these 41 pts we identified mutations in the apoptosis effector BAX in samples from 12 (29%). 20 different BAX mutations were observed across these 12 pts at variant allele frequencies (VAF) consistent with their occurrence in the non-CLL compartment. Mutations included frameshift, nonsense, canonical splice site and missense mutations occurring in key structural elements of BAX consistent with a loss-of-function mechanism (Fig 1A). Interestingly, an enrichment of missense and truncating mutations predicted to escape nonsense mediated decay were observed at the C-terminus of the BAX protein affecting the critical α9 helix. Mutations in this region have previously been shown in cell lines to cause aberrant intracellular BAX localization and abrogation of normal BAX function in apoptosis (Fresquet Blood 2014; Kuwana J Biol Chem 2020). For comparison, NGS targeted sequencing for BAX mutations was performed on samples from cohorts of pts with (i) myeloid or lymphoid malignancy (n=80) or (ii) R/R CLL treated with BTK inhibitors (n=15) after a similar extent of preceding chemotherapy. Neither of these cohorts had previous exposure to Ven. BAX mutations were not detected in any samples from these pts. Longitudinal sampling from pts on Ven harboring BAX mutations in the non-CLL compartment was performed to further understand compartment dynamics over time (in 9 pts over 21-93 months of follow up). Multiple pts demonstrated a progressive increase in VAF of single BAX mutations over time to become clonally dominant within the non-CLL compartment and with observed VAFs consistent with their presence in the myeloid compartment. Mutations in other genes implicated in clonal hematopoiesis and myeloid malignancy including ASXL1, DNMT3A, TET2, U2AF1 and ZRSR2 were also detected in these pts samples. Targeted amplicon single cell sequencing (Mission Bio) demonstrated the co-occurrence of clonally progressive BAX mutations within the same clones as mutations in DNMT3A and ASXL1 as well as the existence of further BAX mutations at low VAF outside these dominant clones which remained non-progressive over time (Fig 1B). In addition, fluctuations in the presence and VAF of myeloid-disease associated mutations was noted with Ven exposure. In aggregate these data are consistent with the existence of a selective pressure within the myeloid compartment of these pts and an interplay of BAX with other mutations in determining survival and enrichment of these clones over time with ongoing Ven therapy. In summary, we have observed the development of BAX-mutated clonal hematopoiesis specifically in pts with CLL treated with long-term Ven. These data are consistent with a multi-lineage pharmacological effect of Ven leading to a survival advantage for clones harboring BAX mutations within the myeloid compartment during chronic Ven exposure. Finally, our data support the further investigation of BAX mutations as a potential resistance mechanism in myeloid malignancies treated with Ven. Disclosures Blombery: Invivoscribe: Honoraria; Amgen: Consultancy; Janssen: Honoraria; Novartis: Consultancy. Anderson:Walter and Eliza Hall Institute: Patents & Royalties: milestone and royalty payments related to venetoclax.. Seymour:Celgene: Consultancy, Honoraria, Research Funding; F. Hoffmann-La Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Janssen: Consultancy, Honoraria, Research Funding; AstraZeneca: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Gilead: Consultancy; Mei Pharma: Consultancy, Honoraria; Morphosys: Consultancy, Honoraria; Nurix: Honoraria; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Tam:Janssen: Honoraria, Research Funding; AbbVie: Honoraria, Research Funding; BeiGene: Honoraria. Huang:Servier: Research Funding; Walter and Eliza Hall Institute: Patents & Royalties: milestone and royalty payments related to venetoclax.; Genentech: Research Funding. Wei:Janssen: Honoraria, Other; Walter and Eliza Hall Institute: Patents & Royalties; AMGEN: Honoraria, Other: Advisory committee, Research Funding; Novartis: Honoraria, Research Funding, Speakers Bureau; Astellas: Honoraria, Other: Advisory committee; Pfizer: Honoraria, Other: Advisory committee; Macrogenics: Honoraria, Other: Advisory committee; Abbvie: Honoraria, Other: Advisory committee, Research Funding, Speakers Bureau; Genentech: Honoraria, Other: Advisory committee; Servier: Consultancy, Honoraria, Other: Advisory committee; Celgene: Honoraria, Other: Advisory committee, Speakers Bureau; Astra-Zeneca: Honoraria, Other: Advisory committee, Research Funding. Roberts:Janssen: Research Funding; Servier: Research Funding; AbbVie: Research Funding; Genentech: Patents & Royalties: for venetoclax to one of my employers (Walter & Eliza Hall Institute); I receive a share of these royalties.

Abstract: Background Mantle cell lymphoma (MCL) is a clinically and pathogenetically distinct B-cell non-Hodgkin lymphoma that presents at a median age of 65 years and typically at an advanced stage. High dose chemotherapy and stem cell transplantation can achieve durable responses, but disease eventually relapses in most patients. Allogeneic transplantation can achieve a cure in some but is only suitable for a minority of younger, fitter patients who achieve remission to salvage but carries risks of GVHD. Bruton tyrosine kinase inhibitors (BTKi) are active in relapsed MCL but the median PFS is generally less than 2 years and ibrutinib failure is associated with particularly poor outcomes (Cheah et al., Ann Oncol 2015). Mutations of TP53 are associated with refractoriness to both chemotherapy and novel agents (Eskelund et al., Blood 2017), and patients with disease harboring these mutations are in particular need of more effective therapies. Promising activity has recently been demonstrated with chimeric antigen receptor T-cells (CAR T), albeit with significant rates of cytokine release syndrome (CRS) and neurotoxicity (Wang et al., New England Journal of Medicine 2020), resulting in FDA approval of brexucabtagene autoleucel in MCL. Rationale Tisagenlecleucel (Novartis) is a CAR T-cell product directed against CD19 that is approved in many countries for the treatment of relapsed DLBCL and ALL. MCL consistently expresses CD19 at diagnosis and relapse and is therefore a promising target. Pre-clinical data suggests synergistic effects if tisagenlecleucel is combined with the BTKi ibrutinib. The proposed mechanism includes enhancing T cell activation and expansion (Fraietta et al., Blood 2016), disrupting the MCL nodal environment (Long et al., The Journal of Clinical Investigation 2017) and mitigating CRS (Ruella et al., Clin Cancer Res 2016). Clinical trials in CLL show that the combination is safe and effective, including deep minimal residual disease negative responses (Gill et al., Blood 2018, Gauthier et al., Hematological Oncology 2019). We hypothesise that combination treatment will be tolerable and improve outcomes in a poor risk MCL population. Combination, time-limited therapy would also avoid the burdens of continuous treatment. Study Design and Methods 20 adult patients with MCL that has relapsed following front-line therapy, or those patients with MCL with TP53 aberrations who have achieved less than complete response on PET imaging after 2 cycles of induction will be enrolled (See Fig 1. for inclusion and exclusion criteria). Treatment consists of 560mg oral ibrutinib followed by a single infusion of tisagenlecleucel. Autologous lymphocytes for CAR T manufacture will be collected after a minimum of 7 days of continuous ibrutinib therapy. Ibrutinib will be continued during CAR T manufacture and for 6 months after infusion (see Fig 2.) Patient characteristics will be presented using descriptive statistics, response rates will be calculated as percentages using exact methods from the binomial distribution, and progression-free survival, duration of response and overall survival will be described using the Kaplan-Meier method. The primary objective is to estimate the complete response (CR) rate at month 4 following tisagenlecleucel infusion in combination with ibrutinib with the primary endpoint being CR rates at month 4 post tisagenlecleucel using the Lugano criteria. Secondary objectives include estimating MRD negative response rates, response rates according to TP53 status, and safety of the combination. Exploratory translational studies include studies of T cell repertoire and phenotype during ibrutinib exposure and after tisagenlecleucel infusion. The role of circulating tumour DNA monitoring in the management of MCL is also being evaluated. The trial is investigator led, sponsored by the Peter MacCallum Cancer Centre, with additional sites throughout Australia. The study was initiated in April 2020 and is actively recruiting patients. The trial is registered at ClinicalTrials.gov: NCT04234061. Disclosures Hamad: Abbvie: Honoraria; Novartis: Honoraria. Blombery:Janssen: Honoraria; Amgen: Consultancy; Invivoscribe: Honoraria; Novartis: Consultancy. Seymour:Nurix: Honoraria; Morphosys: Consultancy, Honoraria; Mei Pharma: Consultancy, Honoraria; Gilead: Consultancy; AstraZeneca: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria, Research Funding; F. Hoffmann-La Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Research Funding; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Tam:Pharmacyclics LLC, an AbbVie Company: Honoraria; BeiGene: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; AbbVie: Honoraria, Research Funding. Dickinson:Janssen: Consultancy, Honoraria, Speakers Bureau; Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau; Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Gilead: Consultancy, Honoraria, Research Funding, Speakers Bureau; Merck Sharp & Dohme: Consultancy. OffLabel Disclosure: Tisagenlecleucel is not currently approved for use in MCL.

Abstract: Background: The phase II AIM trial (Tam et al, NEJM 2018; NCT02471391), using combination BTK inhibitor ibrutinib (IB) and BCL-2 inhibitor venetoclax (VEN) therapy achieved excellent 16 week complete remission rates (CRR) (primary endpoint; 62%) in patients (pts) with poor prognosis mantle cell lymphoma (MCL), higher than currently approved second line IB monotherapy. Additionally, overall response rate (ORR) by PET of 71%, with attainment of minimal residual disease (MRD) negativity was reported. At the time of primary endpoint analysis (median follow up 15.9 months), median progression free survival (PFS), duration of response (DOR), time to progression (TTP) and overall survival (OS) had not been reached. Herein, we update our results with an additional 21.6 months of follow-up and report the outcomes of pts who electively interrupted treatment. Methods: Pts with MCL who had relapsed or refractory disease (R/R; n=23) or were treatment naïve but inappropriate for chemotherapy (n=1) were enrolled. Pts commenced treatment with IB 560mg/d for 4 weeks, followed by weekly ramp-up of VEN to 400mg/d. Initially, pts were intended to continue IB and VEN until progressive disease or unacceptable toxicity; a later amendment allowed pts to electively interrupt both drugs if MRD-negative CR was reached. Pts who elected to interrupt therapy were closely monitored by peripheral blood flow MRD testing and regular CT scans, and were allowed to recommence both study drugs at MRD recrudescence or clinical progression. Results: Median age was 68 years (range, 47-81), median number of previous treatments was 2 (range, 0 to 6), and 50% had aberrations of TP53. As previously reported, the flow MRD-negative and ASO-PCR MRD-negative rates were 67% and 38%, respectively. For the current analysis, the median follow-up was 37.5 months (range, 1.4-45.3).The median DOR and TTP had not been reached and were estimated to be 74% and 60% at 30 months, respectively. The median PFS was 29 months (95% CI of 13-NE) (Figure 1), and the median OS was 32 months (95% CI of 27-NE) (Figure 2). For pts with TP53 aberrant MCL (n=12), the CRR was 50% (95% CI 21-79) with and without PET. In this group the ORR was 58% (95% CI 28-85) without PET and 50% (CI 21-79%) with PET. The DOR in 6 responders with TP53 aberrant MCL (excluding one pt with CRu) was 12+, 24+, 26+, 35+, 36+ and 38+ months from study commencement. In contrast, pts with ATM aberrant MCL (n=10) the CRR was 90% (95% CI 55-100) with and without PET, and the ORR was 90% (95% CI 55-100) with and without PET. Of the 9 responders with ATM aberrant MCL, the DOR was 9+, 9+, 12+, 24+, 31+, 35+, 36+, 37+ and 38+ months from study commencement. Of 13 deaths, 8 were due to PD. Of the other 5 deaths, 2 were due to infection, and 1 each to cardiac failure, glioblastoma, and graft versus host disease after an allograft that occurred after PD on trial. Five pts in MRD negative PET-confirmed CR electively interrupted treatment after a median 18.5 months (range 18-33) of therapy: one pt had radiological progression after 7 months, and the other 4 remained free of clinical or MRD progression after 6, 13, 17 and 18 months off therapy. Conclusions: The median PFS for the IB-VEN combination was 29 months. Treatment interruption was feasible for pts in MRD-negative complete remissions, raising the prospect of limited duration targeted-agent therapy in the management of R/R MCL. Disclosures Handunnetti: Gilead: Honoraria; Abbvie: Other: Travel Grant. Anderson:Walter and Eliza Hall Institute: Employment, Patents & Royalties: Institute receives royalties for venetoclax, and I receive a fraction of these.. Hicks:Clarity: Research Funding; Ipsen: Research Funding; Telix Pharmaceuticals: Equity Ownership. Bressel:Regeneron Pharmaceuticals: Consultancy. Koldej:NanoString Technologies: Other: Travel grant. Ritchie:Amgen: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy; BMS: Research Funding; Takeda: Research Funding; Beigene: Research Funding; Imago: Research Funding; Novartis: Honoraria; Sanofi: Honoraria. Seymour:Roche: Consultancy, Research Funding, Speakers Bureau; Acerta: Consultancy; Takeda: Consultancy; Janssen: Consultancy, Research Funding; Celgene: Consultancy, Research Funding, Speakers Bureau; AbbVie: Consultancy, Honoraria, Research Funding, Speakers Bureau. Roberts:Walter and Eliza Hall Institute: Patents & Royalties: Institute receives royalties for venetoclax, and I receive a fraction of these.; AbbVie: Other: Unremunerated speaker for AbbVie, Research Funding; Janssen: Research Funding; Australasian Leukaemia and Lymphoma Group: Membership on an entity's Board of Directors or advisory committees; BeiGene: Research Funding. Tam:AbbVie: Honoraria, Research Funding; Roche: Honoraria; BeiGene: Honoraria; Novartis: Honoraria; Pharmacyclics LLC, an AbbVie company: Honoraria; Janssen: Honoraria, Research Funding. OffLabel Disclosure: While ibrutinib is FDA approved for use in relapsed and refractory mantle cell lymphoma, venetoclax and combination venetoclax and ibrutinib are not licensed for use in mantle cell lymphoma. The use of venetoclax and ibrutinib for this indication is investigational.