Abstract: DLBCL is the most common subtype of non-Hodgkin lymphoma, constituting 30-40% of all new cases. Lenalidomide (Len) and Avadomide (Ava), small molecule cereblon modulators (CELMoD) with clinical activity in DLBCL, bind to cereblon in the CRL4CRBN E3 ligase, leading to ubiquitination and subsequent degradation of transcription factors Aiolos and Ikaros. Aiolos/Ikaros bind to the promoters of interferon stimulated genes (ISGs) and repress transcription in DLBCL cells. Degradation of these substrates by Len and Ava results in an upregulation of ISG expression leading to decreased proliferation and increased apoptosis of DLBCL cells. Ava is directly cytotoxic against ABC and GCB-DLBCL cells while Len has preferential activity in ABC-DLBCL. To date, our understanding of the COO independent activity of Ava is due to increased kinetics and greater depth of degradation of Aiolos/Ikaros compared to Len. We sought to further understand the biology of these substrates and their transcriptionally repressive activities in DLBCL. Utilizing a comprehensive approach of RNAseq and ChIP-seq of histone modifications (active: H3K27ac, H3K4me3; repressive: H3K27me3 and H3K9me3), we profiled a panel of DLBCL cell lines (2 ABC which are sensitive in proliferation assays to both Len/Ava (TMD8 and U2932), 1 GCB cell line (WSU-DLCL2) which is sensitive only to Ava and an intrinsically resistant GCB cell line (SUDHL-4)). In TMD8 and U2932 (ABC-DLBCL), both Len and Ava treatment resulted in upregulation of ISGs, while only Ava was increased ISG mRNA levels in WSU-DLCL2 (GCB-DLBCL). Neither drug induced ISG expression in the resistant SUDHL-4 (GCB-DLBCL). We found a qualitative association between activity of the drugs and baseline histone modifications of promoters for ISGs with TMD8 and U2932 being relatively enriched for H3K27ac, H3K4me3 and depleted for H3K27me3 and H3K9me3 compared to WSU-DLCL2 and SUDHL-4. SUDHL-4 had the least enrichment for poised and the most enrichment for repressive marks at the transcriptional start sites of ISGs of the cell lines profiled. These data indicate that chromatin modifications, such as decreased active histone marks and increased repressive histone marks at the promoters of ISGs correlate with Len and Ava sensitivity. We hypothesized that Aiolos/Ikaros, known substrates of Len/Ava and repressors of ISGs, were involved in regulation of nearby chromatin landscape through cooperation with transcriptional repressor complexes. To identify complexes associated with these proteins, we performed TMT labeled proteomics on nuclear lysates immunoprecipitated for Aiolos or Ikaros. We identified a significant enrichment in a number of complexes including the nucleosome remodeling deacetylase (NuRD) complex of which HDAC1 and HDAC2 are integral components. Utilizing a protein ligation assay, the interaction of Aiolos/Ikaros with multiple components of the NuRD complex including CHD4, HDAC1 and HDAC2 was confirmed. Across a panel of 10 cell lines 50-80% of cells were positive for a complex formation of Aiolos/Ikaros with a component of the NuRD complex and a majority of these cells were in the G1 phase of the cell cycle. Given the interaction of Aiolos/Ikaros with the NuRD complex, we hypothesized that a combination treatment of Ava with citarinostat (CC-241), a HDAC 1/2/3/6 inhibitor, would result in enhanced ISG expression and synergistic cell autonomous activity in DLBCL. The combination of Ava and CC-241 led to a significant increase in mRNA expression of ISGs such as IFIT3 by 4.2-14 fold and DDX58 by 6.8-8.2 fold compared to either single agent (IFIT3: Ava 0.5-8 fold; CC-241 1.5-1.6 fold p & lt;0.05-0.001; DDX58: Ava 1.5-3 fold; CC-241 2.2-3 fold p & lt;0.05-0.01). CC-241 demonstrated an inhibition of cell proliferation and increased apoptosis in a dose dependent and COO independent manner (1-4 mM) in a panel of DLBCL cell lines. The combination resulted in a synergistic anti-proliferative activity against 6 of 11 DLBCL cell lines profiled. These data demonstrate that Aiolos/Ikaros regulate ISG expression in DLBCL in part through directing epigenetic modifications of their promoters. The combination of Ava with CC-241 results in a synergistic inhibition of DLBCL cell proliferation, through enhanced derepression of transcriptional activity at the promoter regions of ISGs. These data highlight the potential of combining avadomide with a HDAC inhibitor such as citarinostat in DLBCL. Disclosures Hagner: Celgene Corporation: Employment, Equity Ownership, Patents & Royalties. Chiu:Celgene: Employment, Equity Ownership, Patents & Royalties. Chopra:Amgen Inc: Employment; Celgene Corporation: Equity Ownership. Colombo:Celgene: Employment, Equity Ownership. Patel:Celgene: Equity Ownership. Ortiz:Celgene Corporation: Employment, Equity Ownership. Loos:Celgene: Employment, Equity Ownership. Towfic:Celgene Corporation: Employment, Equity Ownership. Waldman:Celgene: Employment, Equity Ownership, Patents & Royalties. Gandhi:Celgene Corporation: Employment, Equity Ownership, Patents & Royalties.

Abstract: The role of haploidentical hematopoietic cell transplantation (HCT) using posttransplant cyclophosphamide (PTCy) for acute lymphoblastic leukemia (ALL) is being defined. We performed a retrospective, multivariable analysis comparing outcomes of HCT approaches by donor for adults with ALL in remission. The primary objective was to compare overall survival (OS) among haploidentical HCTs using PTCy and HLA-matched sibling donor (MSD), 8/8 HLA-matched unrelated donor (MUD), 7 /8 HLA-MUD, or umbilical cord blood (UCB) HCT. Comparing haploidentical HCT to MSD HCT, we found that OS, leukemia-free survival (LFS), nonrelapse mortality (NRM), relapse, and acute graft-versus-host disease (aGVHD) were not different but chronic GVHD (cGVHD) was higher in MSD HCT. Compared with MUD HCT, OS, LFS, and relapse were not different, but MUD HCT had increased NRM (hazard ratio [HR], 1.42; P = .02), grade 3 to 4 aGVHD (HR, 1.59; P = .005), and cGVHD. Compared with 7/8 UD HCT, LFS and relapse were not different, but 7/8 UD HCT had worse OS (HR, 1.38; P = .01) and increased NRM (HR, 2.13; P ≤ .001), grade 3 to 4 aGVHD (HR, 1.86; P = .003), and cGVHD (HR, 1.72; P ≤ .001). Compared with UCB HCT, late OS, late LFS, relapse, and cGVHD were not different but UCB HCT had worse early OS (≤18 months; HR, 1.93; P & lt; .001), worse early LFS (HR, 1.40; P = .007) and increased incidences of NRM (HR, 2.08; P & lt; .001) and grade 3 to 4 aGVHD (HR, 1.97; P & lt; .001). Haploidentical HCT using PTCy showed no difference in survival but less GVHD compared with traditional MSD and MUD HCT and is the preferred alternative donor HCT option for adults with ALL in complete remission.

Abstract: Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare hematological malignancy with a poor prognosis and considered incurable with standard conventional chemotherapy. Small observational studies have shown that allogeneic hematopoietic cell transplantation (allo-HCT) offers durable remissions in patients with BPDCN. We conducted an analysis of 164 patients with BPDCN from 78 centers who underwent allo-HCT between 2007-2018 using data reported to the Center for International Blood and Marrow Transplant Research (CIBMTR). Results: Median follow up of survivors was 49 months (range 6-121). 5-year overall survival (OS), disease-free survival (DFS), relapse, and non-relapse (NRM) rates were 51.2% (95% confidence interval [95%CI]: 42.5-59.8%), 44.4% (95%CI: 36.2-52.8%), 32.2% (95%CI: 24.7-40.3%), and 23.3% (95%CI: 16.9-30.4%), respectively. Disease relapse was the most common cause of death. On multivariate analyses, age ≥60 was predictive for inferior OS (hazard ratio [HR] = 2.16, 95% CI 1.35-3.46, p= 0.001), and higher NRM [HR= 2.19, 95% CI 1.13-4.22, p= 0.02]. Remission status at time of allo-HCT (CR2/PIF/Relapse vs CR1) was predictive of inferior OS [HR= 1.87, 95% CI 1.14-3.06, p= 0.01] and DFS [HR= 1.75, 95% CI 1.11-2.76, p= 0.02]. Use of myeloablative conditioning with total body irradiation (TBI) was predictive for improved DFS and reduced risk of relapse. Conclusion: Allo-HCT is effective in providing durable remissions and long-term survival in BPDCN. Younger age and allo-HCT in CR1 predicted for improved survival, while myeloablative conditioning with TBI predicted for less relapse and improved DFS. Novel strategies incorporating allo-HCT are needed to further improve outcomes.

Abstract: Allogeneic hematopoietic cell transplant is a potential curative therapy for acute lymphoblastic leukemia (ALL). Delineating the graft-versus-leukemia (GVL) effect as a function of graft-versus-host disease (GVHD) offers the potential to improve survival. We examined 5215 transplant recipients with ALL reported to the Center for International Blood and Marrow Transplant Research registry. Overall survival (OS) was compared according to the presence and severity of GVHD and evaluated in 3 cohorts: 2593 adults in first or second complete remission (CR1/CR2), 1619 pediatric patients in CR1/CR2, and 1003 patients with advanced (CR ≥3 or active disease) ALL. For patients in CR1/CR2, development of acute GVHD (aGVHD) or chronic GVHD (cGVHD) was associated with lower risk of relapse than no GVHD (hazard ratio [HR], 0.49-0.69). Patients with advanced ALL developing grades III and IV aGVHD or cGVHD were also at lower risk of relapse (HRs varied from 0.52 to 0.67). Importantly, adult and children in CR1/CR2 with grades I and II aGVHD without cGVHD experienced the best OS compared with no GVHD (reduction of mortality with HR, 0.83-0.76). Increased nonrelapse mortality accompanied grades III and IV aGVHD (HRs varied from 2.69 to 3.91) in all 3 cohorts and abrogated any protection from relapse, resulting in inferior OS. Patients with advanced ALL had better OS (reduction in mortality; HR, 0.69-0.73) when they developed cGVHD with or without grades I and II aGVHD. In conclusion, GVHD was associated with an increased GVL effect in ALL. GVL exerted a net beneficial effect on OS only if associated with low-grade aGVHD in CR1/CR2 or with cGVHD in advanced ALL.

Abstract: HCT entails substantial TRM justifying continued efforts to better risk stratify patients. Single institutional studies have suggested several clinically available biomarkers of CRP, ferritin and albumin influence TRM if not overall survival (OS). We sought to confirm the independent prognostic value of these biomarkers in a large multi-institutional cohort. The study population consisted of 784 adults with AML in remission (80%) or MDS (20%) undergoing unrelated donor HCT between 2008 and 2010 and available cryopreserved samples through the Center for International Blood and Marrow Transplant Research (CIBMTR) repository. CRP and ferritin were centrally quantified by ELISA from cryopreserved plasma whereas albumin levels obtained from center reported data. Correlation studies for biomarkers required log transformation of CRP and ferritin to produce a normal distribution. Multivariate models were fitted separately for each biomarker applying protocol specified thresholds generated from the literature of CRP 〉 10 mg/L, ferritin 〉 2500 ng/mL, albumin 〈 3.5 g/dL on TRM. Further analysis explored optimal cutpoints for this cohort for all significant clinical variables for TRM. HCT characteristics included a median age of 50 (range 18-78) years, HCT-CI (co-morbidity index) 3 or more in 35%, single allele/antigen mismatch (7/8) in 23%, PB as stem cell source in 83%, and myeloablative conditioning in 72%. Biomarker data were available in 783, 781 and 695 cases for CRP, ferritin and albumin respectively. The median values and ranges for each biomarker were as follows: 5.0 mg/L (0.3 - 316) for CRP, 1148 ng/mL (51 – 14,298) for ferritin and 3.6 g/dL (0.6-5.3) for albumin. Log transformed CRP and ferritin showed a modest correlation (r=0.35, P 〈 0.001), and log CRP was marginally associated with albumin (r=-0.12, P=0.002). HCT-CI had no correlation to CRP and albumin. Higher ferritin was associated with HCT-CI (P=0.014) and disease (P 〈 .001). In the entire population, TRM and overall survival (OS) at 2 years were 23% and 54%, respectively. The table shows the independent association of each biomarker with TRM and OS. Ferritin had no association with these outcomes but only 12% had levels above 2500 by ELISA. The optimal cutpoints for TRM were defined as follows: CRP 〉 3.67 (HR=1.75, P=0.001); albumin 〈 3.4 (HR 1.70, P 〈 0.001); and ferritin as a continuous variable (HR 1.30, P = 0.008). A risk score was created modeling optimal biomarker thresholds to predict TRM based on the following formula: risk score = 0.44633*I(CRP 〉 3.67)+0.18330*ln(Ferritin)+0.44730*I(albumin 〈 3.4), where “I” is an indicator function and represent 1 or 0 depending on the presence of the abnormal biomarker level in parenthesis. The risk score included adjustment for HCT-CI. The biomarkers did not influence the incidence of relapse or graft-versus-host disease with any of these models. Elevated CRP and ferritin and decreased albumin prior to HCT were associated with impaired transplant survival, primarily through higher TRM. Integration of a biomarker panel in clinical practice once validated can enhance risk-stratification, improve adjustment for comparative studies and point towards the design of biomarker driven trials. Abstract 422. Table: Multivariate analysis of TRM and OS for biomarkers, and biomarker panel risk score* Abnormal, N (%) Transplant related mortality Overall Survival Biomarker HR 95% CI P HR 95% CI P Protocol defined CRP 〉 10 mg/L 184 (24) 1.52 1.11 – 2.07 0.008 1.22 0.98 – 1.53 0.072 Ferritin 〉 2500 ng/mL 93 (12) 1.26 0.84 – 1.88 0.27 1.15 0.86 – 1.54 0.35 Albumin 〈 3.5 g/dL 290 (42) 1.48 1.10 – 2.0 0.010 1.39 1.13 – 1.72 0.002 Optimal threshold, combined model ** CRP 〉 3.67 mg/L 497 (64) 1.56 1.11 – 2.19 0.010 1.24 1.00 – 1.55 0.054 Log(Ferritin), linear n/a 1.20 0.99 – 1.46 0.07 1.20 1.04 – 1.38 0.010 〈 3.4 g/dL 203 (29.5) 1.58 1.16 – 2.15 0.004 1.37 1.10 – 1.72 0.005 Biomarker Score ** N Low ( 〈 1.5) 200 1.0 - - 1.0 Intermediate (1.5-2.0) 331 1.66 1.10-2.49 0.015 1.38 1.06-1.80 0.017 High ( 〉 2.0) 159 2.72 1.77-4.19 〈 0.001 2.01 1.51-2.70 〈 0.001 * biomarkers adjusted for significant covariates of BMI, disease, mismatch, and CMV serostatus and stratified on conditioning regimen ** combined model includes all biomarkers and HCT-CI Disclosures No relevant conflicts of interest to declare.

Abstract: Background: Imatinib (IM) is the drug of choice for the treatment of Ph+ CML, where a complete cytogenetic response (CCgR) is achieved in more than 80% of early chronic phase (ECP) patients, with a 5-year survival of 90% (Simonsson B, Blood 2005). In the patients who initiated the treatment in late chronic phase (LCP) the response rate is lower and the long-term effect on survival is not yet determined. Aim: We monitored the hematologic, cytogenetic and molecular response to IM in a cohort of 291 patients who were treated with IM in LCP, with focus on progression-free survival and overall survival of complete cytogenetic responders. Methods: Two hundred and ninety-one patients with Ph+ CML in LCP were enrolled in a national prospective study of the GIMEMA CML Working Party in 2001, and were monitored for cytogenetic response and for molecular response every 6 months. Cytogenetics was performed on bone marrow cells with conventional methods. Molecular response was assessed on bone marrow or peripheral blood samples by quantitative PCR (RQ-PCR) using TaqMan methodology and expressing the results as a ratio of BCR-ABL to ABL x100. Patient age ranged from 19 to 82 years (median 52 years). The duration of chronic phase prior to IM treatment ranged from 1 to 202 months (median 38 months). Treatment was IM 400 mg daily through all the study period, with a few exceptions of dose increase to 600 or 800 mg. The median follow-up time after the first IM dose is 62 months. Results: One hundred and sixty patients (55%) achieved a CCgR in 3 to 62 months (median 6 months) after the first IM dose and 126 of them (79%) are still in continuous CCgR after 5 years. For the 160 patients the 5-year survival free from progression to accelerated or blastic phase is 95% and overall survival is 91%. These data are very similar to those reported for the ECP patients in the IRIS study (Simonsson B, Blood 2005). At 5 years, 107 patients were evaluated for molecular response; 62% of them were in major molecular response with a BCR-ABL/ABL ratio lower than 0.10. The BCR-ABL transcript was undetectable in 7 cases by RQ-PCR and in 2 cases by nested PCR. No patient developed heart failure. Conclusions: We confirm that in LCP the CCgR rate to IM is lower than in ECP, but we show that for the complete cytogenetic responders progression-free and overall survival are likely to be as good as for ECP patients, suggesting that the quality of the CCgR is prognostically more important than the duration of leukemia prior to IM treatment. Figure Figure

Abstract: There is a lack of large comparative study on the outcomes of reduced intensity conditioning (RIC) in acute myeloid leukemia (AML) transplantation using fludarabine/busulfan (FB) and fludarabine/melphalan (FM) regimens. Adult AML patients from Center for International Blood and Marrow Transplant Research who received first RIC allo-transplant between 2001 and 2015 were studied. Patients were excluded if they received cord blood or identical twin transplant, total body irradiation in conditioning, or graft-versus-host disease (GVHD) prophylaxis with in vitro T-cell depletion. Primary outcome was overall survival (OS), secondary end points were leukemia-free survival (LFS), nonrelapse mortality (NRM), relapse, and GVHD. Multivariate survival model was used with adjustment for patient, leukemia, and transplant-related factors. A total of 622 patients received FM and 791 received FB RIC. Compared with FB, the FM group had fewer transplant in complete remission (CR), fewer matched sibling donors, and less usage of anti-thymocyte globulin or alemtuzumab. More patients in the FM group received marrow grafts and had transplantation before 2005. OS was significantly lower within the first 3 months posttransplant in the FM group (hazard ratio [HR] = 1.82, P & lt; .001), but was marginally superior beyond 3 months (HR = 0.87, P = .05). LFS was better with FM compared with FB (HR = 0.89, P = .05). NRM was significantly increased in the FM group during the first 3 months of posttransplant (HR = 3.85, P & lt; .001). Long-term relapse was lower with FM (HR = 0.65, P & lt; .001). Analysis restricted to patients with CR showed comparable results. In conclusion, compared with FB, the FM RIC showed a marginally superior long-term OS and LFS and a lower relapse rate. A lower OS early posttransplant within 3 months was largely the result of a higher early NRM.

Abstract: BACKGROUND: Novel agents added to front-line treatments for adult ALL yield high rates of measurable residual disease (MRD) negativity and survival. However, these approaches are infeasible outside large centers and in lower-resource settings. HyperCVAD is commonly used regardless of Philadelphia chromosome (Ph) status but has limitations, particularly in older patients (pts). Because of its efficacy for high-grade lymphomas (NEJM 2013, p. 1915), we hypothesized that DA-EPOCH would be active and safe in adult ALL. METHODS: Details of this study have been reported (ASH 2018, #1519; NCT03023046). Adults with newly-diagnosed ALL were eligible if not candidates for pediatric-inspired therapy (ie, Ph+, age ≥ 40). DA-EPOCH was given with G-CSF (Blood 2002, p. 2685). After treatment of the 1 st 5 pts, the dose-adjustment paradigm was employed once cytopenias were not due to ALL, typically after cycle 2. If Ph+, imatinib (IM) 600 mg or dasatinib (DAS) 100 mg daily on Days 1-14 of each cycle was added. If CD20+, rituximab 375 mg/m 2 was given once per cycle regardless of Ph status. Up to 8 cycles could be given followed by maintenance (POMP ± TKI) or allogeneic transplant (HCT). Pts with WBC & gt; 30K/µL or LDH & gt; 3x upper limit of normal at diagnosis received 10 doses of intrathecal methotrexate as CNS prophylaxis, and others received 8. Response was determined by bone marrow aspirate morphology (morph), multiparameter flow cytometry (MFC) and (for Ph+) BCR-ABL RT-PCR, with complete molecular response (CMR) assigned when the latter was undetectable. When MRD- by MFC (MFC-) per EuroFlow criteria (Leukemia 2010, p. 521), high-throughput sequencing-based MRD testing (HTS; ClonoSEQ) was performed. IKZF1plus was identified by chromosomal microarray as defined previously (JCO 2018, p. 1240). The primary endpoint was rate of MFC- remission within 4 cycles of therapy. Based on an institutional historical rate of MFC- after ≤ 4 cycles of 50% with hyperCVAD + TKI for Ph+ ALL (Am J Hematol 2018, p. 546), we defined success if we observed such remissions in ≥ 70%. A Simon 2-stage design with α = 0.09 and 80% power led to a sample size of 28 pts and success if ≥ 18 were MFC- after ≤ 4 cycles. For Ph-, we enrolled in cohorts (up to 25 total pts) if the upper bound of a 90% confidence interval (CI) stayed ≥ 59%, our historical rate with hyperCVAD. Follow-up provided to 7/1/21. RESULTS: 53/54 enrolled pts were evaluable. Baseline characteristics are in Table 1 and response rates in Table 2. For Ph+ ALL, 20 of 28 pts (71%; 90% CI = 54-85%) reached MFC- after ≤ 4 cycles; TKI used was DAS for 23 pts and IM for 5 pts. In Ph- ALL, 16 of 25 pts (64%; 90% CI = 46-80%) were MFC- after ≤ 4 cycles. Median follow-up of survivors was 22 months (mo; range: 4-50 mo). Median and 2-yr EFS were 15 mo and 32% (respectively); median OS was not reached, and 2-yr OS was 70% (Figure). In those age & gt; 60 yrs, 2-yr EFS was 49% and OS was 71%. In univariate Cox models, neither WBC, age, adverse-risk cytogenetics, IKZF1plus, nor MFC- after ≤ 4 cycles were significantly associated with EFS or OS; the strongest was high-risk WBC with EFS (hazard ratio 2.1, p = 0.068). In sum, 36 pts reached MFC-: relapse occurred in 12 of 23 pts (52%) given maintenance therapy vs 4 of 12 pts (33%) who received HCT (p = 0.48 by Fisher exact test). Of 18 pts without MRD by HTS, 9 (50%) relapsed. None of the 6 pts given blinatumomab for MRD after DA-EPOCH have relapsed. Four pts (8%) had isolated CNS relapse. 44 pts (83%) developed ≥ 1 Grade (Gr) 3+ non-hematologic (heme) AE related to DA-EPOCH, with a mean of 2 per pt. Those seen in ≥ 10% of pts were febrile neutropenia/infection (23 Gr 3, 2 Gr 4); mucositis (7 Gr 3); and ALT increase (6 Gr 3). There was only 1 treatment-related death (2%; gastric hemorrhage). Twelve pts (23%) discontinued due to acute or cumulative toxicity. As for heme AEs in pts treated after cycle 1 (ie, when ALL was not the cause), only 15 pts (34%) had a Gr 4 platelet count at any time. CONCLUSIONS: DA-EPOCH yields comparable response and survival rates (with manageable toxicity) as more logistically-complex therapies in primarily high-risk ALL. When TKI was added for Ph+ disease, rates of MFC- exceeded the predefined threshold for success. Its efficacy and safety profile make it an appealing backbone to which novel agents may be added. Pending results of ongoing multivariable analyses comparing DA-EPOCH to historical treatments, DA-EPOCH could be considered a standard option, particularly in older adults and/or lower-resource settings. Figure 1 Figure 1. Disclosures Cassaday: Pfizer: Consultancy, Research Funding; Kite/Gilead: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Research Funding; Pepromene Bio: Membership on an entity's Board of Directors or advisory committees; Servier: Research Funding; Merck: Research Funding; Vanda Pharmaceuticals: Research Funding. Percival: Abbvie: Research Funding; Nohla Therapeutics: Research Funding; Cardiff Oncology: Research Funding; Glycomimetics: Research Funding; Biosight: Research Funding; BMS/Celgene: Research Funding; Pfizer: Research Funding; Oscotec: Research Funding; Trillium: Research Funding. Halpern: Gilead: Research Funding; Abbvie: Consultancy; Agios Pharmaceuticals: Research Funding; Tolero Pharmaceuticals: Research Funding; Novartis: Research Funding; Bayer: Research Funding; Imago Pharmaceuticals: Research Funding; Jazz Pharmaceuticals: Research Funding; Agios: Consultancy; Nohla Therapeutics: Research Funding; Pfizer: Research Funding. Becker: Glycomimetics: Research Funding; CVS Caremark: Consultancy; Abbie: Research Funding; BMS: Research Funding; Pfizer: Research Funding; Cardiff Oncology: Research Funding; SecuraBio: Research Funding. Oehler: BMS: Consultancy; OncLive: Honoraria; Takeda: Consultancy; Pfizer: Research Funding. Shustov: Seagen Inc.: Research Funding. Orozco: Actinium Pharmaceuticals, Inc.: Other: site PI for clinical trial(s) sponsored by Actinium, Research Funding. Walter: BMS: Consultancy; Astellas: Consultancy; Agios: Consultancy; Amphivena: Consultancy, Other: ownership interests; Selvita: Research Funding; Pfizer: Consultancy, Research Funding; Jazz: Research Funding; Macrogenics: Consultancy, Research Funding; Immunogen: Research Funding; Celgene: Consultancy, Research Funding; Genentech: Consultancy; Janssen: Consultancy; Kite: Consultancy; Aptevo: Consultancy, Research Funding; Amgen: Research Funding. Radich: Amgen: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Genentech: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees. OffLabel Disclosure: Rituximab is not FDA approved for the treatment of acute lymphoblastic leukemia.

Abstract: BACKGROUND: CNS directed chemotherapy (chemo) reduces the risk of CNS relapse of ALL, but the optimal way to measure baseline CNS involvement is controversial. Baseline CSF testing can provide risk stratification and often dictates CNS prophylaxis (ppx) during initial treatment. Despite advances, up to 10% of adults still suffer CNS relapse (Blood 2008;112:1646, Cancer 2014;120:3660). Testing typically focuses on conventional cytospin (CC) of CSF, but CC is limited by interobserver variability and insensitivity (Blood 2014;124:3799). Alternatively, MFC is more sensitive (ASH 2018, #658). A previous study in children with ALL found leukemia detection in the CNS by CC or MFC at diagnosis to be associated with an increased risk of both isolated bone marrow and any CNS relapse (ASH 2018, #657). To our knowledge, this use of MFC has not specifically been studied in hyperCVAD, a commonly used chemotherapy regimen for the initial treatment of adult ALL. We hypothesized that baseline lymphoblast detection in the CSF by MFC is predictive of CNS relapse. METHODS: We included data collected from 11/6/07 to 6/22/20. Patients (pts) ≥18 years old who received ≥4 cycles (equivalent of cycle 2B) of hyperCVAD as first-line therapy were eligible. Pts must have had MFC done on CSF at baseline. Pts with mixed phenotype or insufficient follow-up data were excluded. CNS ppx with hyperCVAD historically uses intra-CSF (ie, intrathecal or intraventricular) methotrexate 12 mg on day 2 and cytarabine 100 mg on day 8 of each cycle for 6-12 doses without cranial radiation, though all patients were treated per physician discretion. CC and MFC results were taken from clinical reports and verified by an independent hematopathologist (Dr. Cherian). Baseline CSF positivity (CSF+) and negativity (CSF-) were defined by MFC, with any percentage of lymphoblasts considered CSF+. COG definitions of CNS status by CC were also used (J Clin Oncol 2016;34:2380). Univariate Cox models evaluated associations to CNS relapse. Kaplan-Meier curves were used to estimate the probabilities of overall survival (OS) and cumulative incidence of CNS relapse. RESULTS: We identified 92 eligible pts. Disease and treatment characteristics are summarized in Table 1, and results of initial CSF testing are shown in Table 2. Twenty-one pts were CSF+ by MFC at baseline: by CC, 6 of these were positive, 6 were negative, 7 were equivocal (ie, morphologic review was unable to rule out blasts), and 2 did not have baseline CC. None were positive by CC but negative by MFC. Eight of 29 (38%) with circulating blasts had a traumatic ( & gt;10 RBC/uL of CSF) first lumbar puncture (LP). Of these 8, 4 (50%) were CSF+. Five (5%) pts had an Ommaya reservoir placed during treatment. Pts received a median of 8 doses of intra-CSF chemo (range, 5-52). All but 7 pts (8%) received a combination of methotrexate and cytarabine like above. Twenty CSF+ pts (95%) achieved CSF- after a median of 1 dose of intra-CSF chemo (range, 1-5). Out of the 71 CSF- pts, none became CSF+ during initial treatment despite being tested a median of 5 times (range, 2-10). Eight pts (9%) had CNS relapse (3 isolated, 5 concurrent medullary relapse). Comparisons between baseline CSF testing, intra-CSF treatment, and CNS relapse are shown in Table 2. CSF+ pts received significantly greater doses of intra-CSF chemo. Of the 21 CSF+ pts, 5 (24%) had CNS relapse (2 isolated, 3 concurrent), and out of the 71 CSF- pts, 3 (4%) had CNS relapse (1 isolated, 2 concurrent; p=0.014). Among univariate models of CSF+ vs -, traumatic LP vs not, B vs T lineage, LDH, and WBC, only CSF+ was significantly associated with CNS relapse (hazard ratio 4.8, 95% confidence interval [CI] 1.2-20, p=0.031). Estimated 3-year cumulative incidence of CNS relapse for CSF+ was 15% vs 3.3% for CSF- (Figure 1). Median OS for the whole cohort was not reached, with estimated 3-year OS of 74% (95% CI, 65%-84%). CONCLUSIONS: MFC of CSF is more predictive of CNS relapse risk than CC in the context of front-line hyperCVAD, questioning the use of CC if MFC is performed. Further, CNS relapses were significantly more frequent when CSF+ despite administration of significantly more intra-CSF chemo. Traumatic LP per se did not increase risk of CNS relapse if CSF- by MFC. Surveillance during treatment by MFC in CSF- pts identified no cases of occult CNS relapse, arguing against this routine practice. Future studies should consider incorporating MFC of CSF into risk-adapted CNS-directed treatment strategies. Disclosures Shustov: Seattle Genetics: Research Funding. Becker:Accordant Health Services/Caremark: Membership on an entity's Board of Directors or advisory committees; Cardiff Oncology: Research Funding; SecuraBio: Research Funding; Novartis: Research Funding; Pfizer: Research Funding; JW Pharmaceutical: Research Funding; Glycomimetics: Research Funding; Abbvie: Research Funding; Bristol Myers Squibb: Research Funding; Invivoscribe: Research Funding. Oehler:Takeda: Consultancy; BMS: Consultancy; Pfizer, Inc: Research Funding. Halpern:Bayer: Other; Novartis: Other; Jazz Pharmaceuticals: Other; Imago BioSciences: Other; Tolero Pharmaceuticals: Research Funding. Walter:Amgen: Consultancy, Research Funding; Arog: Research Funding; Argenx: Consultancy; Aptevo: Consultancy, Research Funding; Amphivena: Current equity holder in publicly-traded company; Agios: Consultancy, Research Funding; StemLine: Research Funding; Selvita: Research Funding; Seattle Genetics: Research Funding; Race Oncology: Consultancy; Pfizer: Consultancy, Research Funding; New Link Genetics: Consultancy; Macrogenics: Research Funding; Kite: Consultancy; Jazz: Consultancy, Research Funding; ImmunoGen: Research Funding; Genentech: Consultancy; Daiichi: Consultancy; Celgene: Consultancy, Research Funding; Boston Biomedical: Consultancy; BiVictriX: Consultancy; BioLineRx: Consultancy, Research Funding; Astellas: Consultancy. Godwin:Pfizer Inc.: Research Funding; Immunogen Inc.: Research Funding. Cassaday:Kite/Gilead: Consultancy, Research Funding; Merck: Research Funding; Seattle Genetics: Current Employment, Current equity holder in publicly-traded company; Amgen: Consultancy, Research Funding; Vanda Pharmaceuticals: Research Funding; Pfizer: Honoraria, Research Funding.