Abstract: Abstract 3578 Introduction: Chronic lymphocytic leukemia (CLL) patients bearing 13q14 deletion are known to experience a more favorable clinical course. Recent studies, focusing on patients with loss of 13q as the sole cytogenetic aberration at diagnosis (del13q-only cases), showed that the number of malignant cells carrying this genetic lesion correlates with a more aggressive clinical behavior. However, whether the size of the 13q deletion may also influence the clinical outcome remains to be elucidated. Patients and Methods: Probes for chromosome 13q (LSI-RB1, LSI-D13S319), 11q (LSI-ATM), 17p (LSI-p53) and chromosome 12 (CEP12) were utilized on nuclei collected at diagnosis from: i) a multi-institutional CLL cohort (342 del13q-only cases) and ii) a consecutive unselected single-institution cohort of 265 cases. RB1 deleted cases (delRB1) were defined as having at least 5% of deleted nuclei. Time to treatment (TTT) intervals, as well as Rai staging, IGHV mutational status, CD38 and ZAP70 expression, B2-microglobulin levels, all evaluated at diagnosis, were also available for all cases that entered the study. Genome wide DNA profile was performed in a pilot series of 90 CLL samples using Affymetrix GeneChip Human SNP6 arrays. Results: According to genome wide DNA analysis, delRB1 occurred in a proportion of del13q-only cases (36/90; 40%), always comprising the deleted region detected with the LSI-D13S319 probe (that covers the miR-15a/16-1 cluster and the DLEU2 gene) and characterized by a larger chromosome loss (median size 2.07 Mb vs. a median size of 0.86 Mb for the canonical del13S319). Maximally selected log-rank statistics identified the 70% of nuclei bearing del13S319 as the most appropriate cut-off value capable of separating del13q-only cases into two subgroups with different TTT distributions. Consistently, del13q-only cases with at least 70% of nuclei bearing del13S319 showed a significantly shorter TTT than del13q-only cases with less than 70% deleted nuclei (p=0.0001). Del13q-only cases were then divided in four subsets according to the percentage of nuclei bearing del13S319 with or without a concomitant delRB1: del13S319 〈 70% (group 1), 144 cases; del13S319 〈 70% + delRB1 (group 2), 95 cases; del13S319 〉 70% (group 3), 64 cases; del13S319 〉 70% + delRB1 (group 4), 39 cases. The median TTT of group 1 (not reached) was significantly longer than the median TTT of group 2 (92 months, p=0.012), group 3 (68 months, p 〈 0.0001), and group 4 (82 months, p=0.0025; see Fig. 1A). Multivariate Cox proportional hazard analyses selected the presence of delRB1 (p=0.029), along with the IGHV mutational status (p 〈 0.0001), as an independent negative prognosticator in the context of del13q-only cases with low/intermediate Rai risk (Rai stage of 0/I at diagnosis) and 〈 70% of del13S319. Cases belonging to the consecutive unselected single-institution CLL cohort were divided into subsets according to the classification proposed by Döhner et al (NEJM, 2000). Notably, the presence of del13S319 in 〈 70% of cells in the absence of delRB1 identified a patient subset with particularly stable and benign clinical course (group A in Fig. 1B, 48 cases; median TTT not reached). Conversely, patients characterized by del13S319 in 〈 70% of cells but with a larger deletion, as determined by concomitant delRB1 (group B, 24 cases), or del13S319 in 〉 70% of cells (with or without delRB1, group C, 25 cases) or a normal karyotype (group D, 75 cases) had shorter median TTT intervals (ranging from 105 to 129 months, p 〈 0.01 in all the comparisons). Finally, patients affected by CLL bearing trisomy 12 (group E, 48 cases) and del11q or del17p (group F, 45 cases) experienced the worst clinical courses (p 〈 0.0001). Conclusion: In the context of del13q-only cases, different clinical outcomes were associated to the percentage of 13q14 deleted cells, as well as to the size of the 13q14 deletion, as detected by the LSI-RB1 probe. Moreover, the presence of delRB1 emerged as a feature capable of refining the prognostic assessment in the context of CLL cases with 〈 70% del13S319. The underlying genetic mechanisms correlated with the different clinical outcomes and associated with the size of the 13q deletion are presently under investigation. Disclosures: No relevant conflicts of interest to declare.

Abstract: Abstract 1371 Background: IGHV1-69 gene identifies the most frequent IGHV gene in chronic lymphocytic leukemia (CLL) and identifies the paradigm of unmutated CLL (U-CLL), being used in roughly 1/3 U-CLL. It is often rearranged to form subsets of stereotyped HCDR3 patterns, likely selected and transformed from the natural naïve B-cell repertoire (Blood. 2010; 115:71-7). Being unmutated, IGHV1-69 CLL are hypothetically expected to have competent tumor B-cell receptors (BCR) and to progress more rapidly. However, it has not been investigated if progression occurs similarly in all the subsets. Aims: we aimed to investigate the prognostic significance of mutational status and of stereotypic B-cell receptors in IGHV1-69+ CLL. Methods: Nucleotide sequences of the tumor IGHV1-69/D/J rearrangement, clinical and molecular prognostic parameters at diagnosis and clinical status at follow-up of 294 IGHV1-69+ CLL patients were obtained from 22 hematological Institutions in Italy. CLL B-cell derived IGHV1-69 rearrangements were scanned for HCDR3 stereotypic patterns and assigned to subsets according to the criteria by Murray et al (Blood. 2008; 111: 1524–1533). Enpoint of outcome was time to progression requiring first treatment according to NCI criteria (TTFT) in Rai stage 0 CLL. Results: Of 294 IGHV1-69+ CLL, 264 (89,8%) were unmutated, 168 (57,1%) were assigned to subsets, of which subsets 7 (n=23, 7,8%), 6 (17, 5,8%), 3 (13, 4,4%), 5 (10, 3,4%) and 9 (10, 3,4%) were the most frequent. CD38, ZAP70, normal or sole del13, +12, del11 and del17p scored positive in 109/264 (58,7%), 139/245 (56,7%), 128/248 (50,5%), 51/248 (20,6%), 43/248 (17,3%) and 34/248 (13,7%). CLLs were reclassified as 18 (6,1%) clinical MBL, 101 (34,4%) Rai 0, 155 (52,7%) Rai I-II and 20 (6,8%) Rai III-IV CLL. Subset 6 was also UM in 16/17 (94,1%) cases. Prevalence of CD38 (p 〈 .001), ZAP70 (p=.016), normal or sole del13 (p 〈 .001), +12 (p=.026), del11 (p=.011), and clinical high risk CLL (p=.025) were lower in IGHV1-69 M-CLL than in IGHV1-69 U-CLL. TTFT was significantly shorter in stage 0 IGHV1-69 U-CLL than in IGHV1-69 M-CLL (49 vs 144 months, p 〈 .001, while it was not different between CLL assigned or not to subsets (65 vs 55 months, p=.346). However, specific analysis of individual subsets revealed differential outcomes (p=.005). Among all, it emerged that subset 6 had a TTFT equivalent to IGHV1-69 M-CLL (p=.29) and significantly longer than stage 0 IGHV1-69 U-CLL (median not reached vs 48 months, p=.017). Conclusions: our analysis documents and confirms that unmutated status of IGHV, and not stereotypy, is a relevant prognosticator of outcome (TTFT) in CLL. In the IGHV1-69 CLL it exclude a role of IGHV gene use for CLL progression. However, the good prognosis of Rai 0 U-CLL assigned to subset 6 suggests a differential clinical benign course of this particular subset, irrelevant of unmutated status. One possibility is that the IGHV1-69/D3-16/J3 rearrangements of subset 6 produce a tumor-specific BCR with stereotypic HCDR3 patterns that are anergized by antigen while circulating in the peripheral blood in early stage (Rai 0) CLL. Disclosures: No relevant conflicts of interest to declare.

Abstract: Abstract 464 Fludarabine-refractoriness of chronic lymphocytic leukemia (CLL) is due to TP53 disruption in ∼40% of refractory cases, but in a sizeable fraction of patients the molecular basis of this aggressive clinical phenotype remains unclear. Our initial findings from whole exome sequencing of fludarabine-refractory CLL led to the identification of recurrent mutations of SF3B1, a critical component of the cell spliceosome, prompting further investigations of these alterations in a large CLL panel. The study population comprised 3 clinical cohorts representative of: i) fludarabine-refractory CLL (n=59), including cases (n=11) subjected to whole exome sequencing; ii) newly diagnosed and previously untreated CLL (n=301); and iii) clonally related RS (n=33). Tumor samples were obtained: i) for fludarabine-refractory CLL, immediately before starting the treatment to which the patient eventually failed to respond; ii) for newly diagnosed and previously untreated CLL, at disease presentation. All RS studies were performed on RS diagnostic biopsies. Mutation analysis of SF3B1 was performed on genomic DNA by a combination of Sanger sequencing and targeted next generation sequencing. SF3B1 was altered in 10/59 (17%) fludarabine-refractory CLL by missense mutations (n=9) or in-frame deletions (n=1) clustering in the HEAT3, HEAT4 and HEAT5 repeats of the SF3B1 protein. Two sites that are highly conserved inter-species (codon 662 and codon 700) were recurrently mutated in 3 and 5 cases, respectively. SF3B1 mutations were monoallelic, and were predicted to be functionally significant according to the PolyPhen-2 algorithm. Mutations occurred irrespective of IGHV mutation status, CD38 expression and ZAP70 expression. At the time of fludarabine-refractoriness, SF3B1 mutations were enriched in cases harboring a normal FISH karyotype (p=.008) and distributed in a mutually exclusive fashion with TP53 disruption (mutual information I =0.0609; p=.046). By combining SF3B1 mutations with other genetic lesions enriched in chemorefractory cases (TP53 disruption, NOTCH1 mutations, ATM deletion), fludarabine-refractory CLL appeared to be characterized by multiple molecular alterations that, to some extent, are mutually exclusive. We then compared the prevalence of mutations observed at the time of fludarabine-refractoriness to that observed in other disease phases. At diagnosis, SF3B1 mutations were rare (17/301; 5%), and showed a crude association with short treatment free survival (p 〈 .001) and overall survival (p=.011). Remarkably, 5/17 (29%) CLL mutated at diagnosis were primary fludarabine-refractory patients. In CLL investigated at diagnosis, the hotspot distribution and molecular spectrum of SF3B1 mutations, as well as their mutual relationship with other genetic lesions, were similar to those observed in fludarabine-refractory CLL. SF3B1 mutations were restricted to 2/33 (6.0%) clonally-related RS. Across the different disease phases investigated, mutations were somatically acquired in all cases (n=18) for which germline DNA was available. These data document that mutations of SF3B1, a splicing factor that is a critical component of the spliceosome; i) recurrently associate with fludarabine-refractory CLL; ii) occur at a low rate at CLL presentation; iii) play a minor role in RS transformation, corroborating the notion that CLL histologic shift is molecularly distinct from chemorefractory progression without RS transformation. The identification of SF3B1 mutations points to the involvement of splicing regulation as a novel pathogenetic mechanism in CLL. The pathogenicity of SF3B1 mutations in CLL is strongly supported by clustering of these mutations in evolutionarily conserved hotspots localized within HEAT domains, which are tandemly arranged curlicue-like structures serving as flexible scaffolding on which other components can assemble. Also, the observation that SF3B1 regulates the alternative splicing program of genes controlling cell cycle progression and apoptosis points to a potential contribution of SF3B1 mutations in modulating tumor cell proliferation and survival. In addition to pathogenetic implications, SF3B1 mutations might also provide a therapeutic target for SF3B1 inhibitors, that are currently under pre-clinical development as anti-cancer drugs. Disclosures: No relevant conflicts of interest to declare.

Abstract: Novel therapies targeting BTK (ibrutinib), PI3Kδ (idelalisib) and BCL2 (venetoclax) are active in poor-risk chronic lymphocytic leukemia (CLL) and are widely administered to patients with relapsed/refractory (R/R)-CLL. Given the activity of ibrutinib in high-risk CLL patients, including those with del17p/TP53 mutation or germline IGHV genes, we assumed that this drug could diminish the prognostic utility of the CLL-IPI, because the outcome of patients with high- and very high-risk CLL-IPI scores may improve. Recently, Soumerai et al (Lancet Hematology, 2019) proposed a new risk score for overall survival (OS) based on four accessible markers, called BALL (β2-microglobulin, anemia, LDH, last therapy), in the setting of R/R-CLL patients receiving chemo-immunotherapy or targeted therapies in clinical trials. This model segregates CLL patients into three groups with significantly different OS. This multicenter, observational retrospective study aimed at validating the proposed BALL score for R/R-CLL real-world patients treated with ibrutinib. The primary objectives were to determine whether: i) the BALL score is of prognostic value for ibrutinib R/R-CLL patients, ii) the BALL score is predictive of progression-free survival (PFS); and iii) the CLL-IPI retains its prognostic power also in R/R patients treated with ibrutinib. This study, from an institutional Italian multicenter working group on CLL ('Campus CLL'), included CLL patients collected from 18 Italian centers and 1 Israeli center, who received ibrutinib 420 mg/day outside of clinical trials as salvage therapy with available data for the calculation of the BALL and CLL-IPI scores at the time of the start of treatment. OS was estimated for all subgroups according to both scores. Additionally, risk-specific PFS was assessed. Kaplan-Meier curve, log-rank test and Cox regression analyses were performed. The prognostic accuracy of the predictive model was assessed by the Harrell's C-index. Overall, 541 CLL patients were included in this analysis. The majority of patients were Binet stages B and C (87.2%). The median age was 70.4 years (range 37 - 88) and 353 cases (65.2%) were male. The median number of previous therapies was 2 (range 1-9). The baseline patients' features are listed in Table 1. After a median follow-up of 1.8 years (range 1 month to 5.8 years), 101 patients had died and 206 experienced an event (death or progression). According to the BALL score, 372 patients (68.8%) were classified as low-risk, 132 (24.4%) as intermediate-risk and 37 (6.8%) as high-risk. Stratification of patients according to the BALL score predicted significant differences in terms of OS. Thus, low-risk patients had a 2-year OS probability of 89.2% (HR=1), intermediate-risk of 79.9% (HR=2.8, 95%CI 1.8-4.4, P 〈 0.0001) and high-risk of 48.2% (HR=6.6, 95%CI 3.9-11, P 〈 0.0001) (Figure 1). The C-statistic was 0.66 (P 〈 0.001) for OS prediction. The CLL-IPI score indicated that 32 patients (5.9%) were classified as low-risk, 123 (22.7%) as intermediate-risk, 252 (46.6%) as high-risk and 134 (24.8%) as very high-risk. Stratification of patients according to the CLL-IPI score did not allow to predict significant differences in OS. Indeed, low-risk patients had a 2-year OS probability of 92.7% (HR=1), intermediate-risk patients of 88.4% (HR=2.3, 95%CI 0.5-9.9, P=0.26), high-risk of 84% (HR=3.3, 95%CI 0.8-13.7, P=0.1) and very high-risk of 76.4% (HR=4.3, 95%CI 1.038-17, P=0.046). Both the BALL and CLL-IPI scores failed to stratify patients significantly in terms of PFS. Our multicenter retrospective study confirms the prognostic power of the BALL score in this real-world series of R/R-CLL patients treated with ibrutinib, as previously reported in the setting of clinical trials (Soumerai et al, Lancet Hematology 2019). Furthermore, the CLL-IPI did not retain a discriminative power in the current retrospective study of ibrutinib-treated patients, possibly due to i) the well-known activity of ibrutinib in high-risk CLL patients, i.e. those with TP53 disruption and/or germline IGHV genes, which represent the most heavily weighted adverse risk factors contributing to the CLL-IPI, and to ii) the fact that the CLL-IPI was designed for patients receiving front-line chemo-immunotherapy. Conversely, the BALL score may identify higher risk R/R-CLL patients potentially requiring alternative and more effective therapeutic strategies. Disclosures Mauro: Jannsen: Consultancy, Research Funding; Gilead: Consultancy, Research Funding; Abbvie: Consultancy, Research Funding; Shire: Consultancy, Research Funding; Roche: Consultancy, Research Funding. Coscia:Gilead: Membership on an entity's Board of Directors or advisory committees; Karyopharm Therapeutics: Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Abbvie: Membership on an entity's Board of Directors or advisory committees. Herishanu:Roche: Honoraria; Janssen: Honoraria; AbbVie: Honoraria. Varettoni:ABBVIE: Other: travel expenses; Roche: Consultancy; Gilead: Other: travel expenses; Janssen: Consultancy. Rigolin:AbbVie: Speakers Bureau; Gilead: Speakers Bureau; Gilead: Research Funding. Rossi:Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Abbvie: Honoraria, Other: Scientific advisory board; Janseen: Honoraria, Other: Scientific advisory board; Roche: Honoraria, Other: Scientific advisory board; Astra Zeneca: Honoraria, Other: Scientific advisory board. Gaidano:AbbVie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Sunesys: Consultancy, Honoraria; Astra-Zeneca: Consultancy, Honoraria. Cuneo:Amgen: Honoraria; Abbvie: Honoraria, Speakers Bureau; Gilead: Honoraria, Speakers Bureau; Janssen: Honoraria, Speakers Bureau; Roche: Honoraria, Speakers Bureau. Foà:Roche: Consultancy, Speakers Bureau; Celltrion: Membership on an entity's Board of Directors or advisory committees; Abbvie: Consultancy, Speakers Bureau; Amgen Inc.: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen Inc.: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Shire: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Roche: Consultancy, Speakers Bureau; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Shire: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Abbvie: Consultancy, Speakers Bureau; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celltrion: Membership on an entity's Board of Directors or advisory committees.

Abstract: To compare the capacity of ibrutinib (IB) and idelalisib‐rituximab (IDELA‐R) of prolonging overall survival (OS) as in CLL patients, previously treated with chemotherapy only. Methods A real‐life cohort of 675 cases has been identified and investigated in the database of the groups participating in the study. Results At an unadjusted univariate analysis, a significant death risk reduction was observed favoring IB (IDELA‐R vs IB HR = 0.5, 95% CI = 0.36‐0.71) although with some limitations due to the non‐randomized and retrospective nature of the study and to the lower number of patients in the IDELA‐R group (112 cases) related to the current prescribing practice. To overcome the potential problem of confounding by indication, we adjusted the association between the type of therapy and mortality for all variables significantly associated with OS at Cox univariate analysis. Furthermore, those variables, differently distributed between the two study groups, were introduced into the multivariate Cox model to improve the effectiveness of the analysis. By introducing all these variables into the multiple Cox regression model, we confirmed the protective effect of IB vs IDELA‐R (HR = 0.67, 95% CI = 0.45‐0.98, P  = .04) independent of potential confounders. Conclusions Although our analysis presents some constraints, that is, the unavailability of additional potential confounders, and the retrospective nature of the study, this observation may be of help for the daily clinical practice, particularly in the absence of randomized trials comparing the two schedules.