Parikh, Sameer A.

Abstract Introduction Transformation of chronic lymphocytic leukemia (CLL) into Hodgkin lymphoma (HL) is a rare, but recognized complication of CLL. The prognosis of CLL with HL Transformation (HT) appears significantly worse than de novo HL, but most series are small and there are limited published data. These reports have prompted several groups to recommend aggressive therapy with stem cell transplantation (SCT) in first complete remission (CR1). We describe the largest reported series of HT patients (pts) with analyses of the clinicobiologic characteristics, treatment patterns, and clinical outcomes based upon our multi-institutional clinical experience. Methods Pts diagnosed with HT from 01/2000 - 01/2018 were retrospectively identified in 13 tertiary cancer centers. Clinicobiologic characteristics, treatment type, and survival outcomes for each pt were analyzed. Overall survival (OS) was measured from the time of HT diagnosis until time of death. OS estimates were calculated using the Kaplan-Meier method. The log-rank test was used to calculate differences in survival. Results Ninety-four pts with HT were identified. Median age at HT was 67 years (yrs; range, 38-85) and 81% of the pts were male. Median time from CLL diagnosis to HT was 5.5 yrs (range, 0-20.2; 7 pts with simultaneous diagnosis of CLL and HL). At initial CLL diagnosis, 31%, 34%, 21%, 10%, and 4% were Rai Stage 0, 1, 2, 3, and 4, respectively. At CLL diagnosis, 67% (25/37) had an un-mutated IgVH gene, 36% (21/59) had del(13q), 32% (14/44) had trisomy 12, 24% (14/59) had del(11q), and 15% (9/61) had del(17p). Prior to HT diagnosis, pts had a median of 2 (range, 0-12) therapies for CLL. Seventeen (18%) had no prior CLL treatments. Forty-three (46%) and 25 (27%) patients had received purine analogue- and ibrutinib-based therapy prior to HT, respectively. Baseline characteristics at HT are described in Table 1. As initial therapy for HL, the majority of pts (61%, n = 62) received ABVD-based regimens (adriamycin, bleomycin, vinblastine, and dacarbazine) at full (n = 48) or reduced (n = 14) doses. Of these, CD20 monoclonal antibody was added in 6 and Bruton-tyrosine kinase inhibitor was added in 2. Ten (11%) received a brentuximab-based regimen. Seven (7%) received an RCHOP-based regimen (rituximab, cyclophosphamide, doxorubicin, vincristine, prednisone). Six patients (6%) received no therapy for HT due to frailty. Subsequent therapy included autologous SCT and allogeneic SCT in 7 (7%) and 11 (12%) of patients, respectively. Two (2%) and 5 (5%) pts received their autologous and allogeneic SCT while in CR1, respectively. The median number of treatments for HT per pt was 1 (range, 0-5) with 59 (61%) pts only receiving one line of therapy. After HT diagnosis, pts had a median follow-up of 1.6 yrs (range, 0.0 - 15.1). Two-yr OS after HT diagnosis was 72% (95%CI 62 - 83%). The pts who received any CLL directed therapy (n = 80) prior to HT had a significantly lower estimated 2-yr OS of 69% (95%CI 58 - 82%) compared with pts who did not receive any prior CLL-directed therapy (n = 17; 93%; 95%CI 82-100%; p 0.02; Figure 1). Pts who received purine-analogue-based therapy for their CLL prior to HT had a significantly lower estimated 2-yr OS of 60% (95%CI 46 - 79%) compared with pts who did not receive purine-analogue-based CLL-directed therapy prior to HT (n = 51; 83%; 95%CI 73 - 96%; p 0.009; Figure 2). Although limited by small sample size, the pts who underwent SCT for HT in CR1 had a similar 2-yr OS (n = 7; 67%; 95%CI 38-100%) to pts who did not undergo SCT for HT in CR1 (n = 87; 72%; 95%CI 63 - 84%; p 0.46; Figure 3). Conclusions In this retrospective analysis, we describe the largest reported series of pts with HT from CLL. Two-yr survival in pts with HT was shorter than what is historically expected in patients with de novo HL, but longer than what is expected in CLL pts who transform to diffuse large B-cell lymphoma. Pts with HT who have received prior CLL-directed therapies (specifically purine-analogue-based treatments) are estimated to have a shorter 2-yr OS, likely due to underlying immunosuppression. The majority of pts (61%) only received 1 line of HL therapy and only 20% went on to receive SCT (7% while in CR1), indicating that these patients can have prolonged OS after achieving response to first-line therapy for HT and may not require SCT in CR1. Further study of this rare population is required to determine optimum management. Disclosures Kander: AstraZeneca: Consultancy. Parikh:Gilead: Honoraria; AstraZeneca: Honoraria, Research Funding; Abbvie: Honoraria, Research Funding; Janssen: Research Funding; MorphoSys: Research Funding; Pharmacyclics: Honoraria, Research Funding. Shadman:Acerta Pharma: Research Funding; Verastem: Consultancy; Celgene: Research Funding; Gilead Sciences: Research Funding; Mustang Biopharma: Research Funding; Pharmacyclics: Research Funding; AstraZeneca: Consultancy; Beigene: Research Funding; Genentech: Research Funding; Qilu Puget Sound Biotherapeutics: Consultancy; AbbVie: Consultancy; TG Therapeutics: Research Funding; Genentech: Consultancy. Pagel:Pharmacyclics, an AbbVie Company: Consultancy; Gilead: Consultancy. Mato:Portola: Research Funding; AstraZeneca: Consultancy; Acerta: Research Funding; Prime Oncology: Honoraria; Regeneron: Research Funding; Celgene: Consultancy; Pharmacyclics, an AbbVie Company: Consultancy, Research Funding; Medscape: Honoraria; TG Therapeutics: Consultancy, Research Funding; Johnson & Johnson: Consultancy; AbbVie: Consultancy, Research Funding. Hill:Amgen: Research Funding; Abbvie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Genentech: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Abbvie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees. Danilov:Verastem: Consultancy, Research Funding; Aptose Biosciences: Research Funding; Takeda Oncology: Research Funding; Genentech: Consultancy, Research Funding; TG Therapeutics: Consultancy; Bayer Oncology: Consultancy, Research Funding; Astra Zeneca: Consultancy; Gilead Sciences: Consultancy, Research Funding. Phillips:Abbvie: Research Funding; Bayer: Consultancy; Gilead: Consultancy; Genentech: Consultancy; Pharmacyclics: Consultancy, Research Funding; Seattle Genetics: Consultancy. Brander:Pharmacyclics, an AbbVie Company: Consultancy, Honoraria, Research Funding; AbbVie: Consultancy, Honoraria, Other: Institutional research funding for non investigator initiated clinical trial, Research Funding; Acerta: Other: Institutional research funding for non investigator initiated clinical trial, Research Funding; Novartis: Consultancy, Other: DSMB; Teva: Consultancy, Honoraria; TG Therapeutics: Consultancy, Honoraria, Other: Institutional research funding for non investigator initiated clinical trial, Research Funding; DTRM: Other: Institutional research funding for non investigator initiated clinical trial, Research Funding; Genentech: Consultancy, Honoraria, Other: Institutional research funding for non investigator initiated clinical trial, Research Funding; BeiGene: Other: Institutional research funding for non investigator initiated clinical trial, Research Funding. Smith:BMS: Consultancy; Portola: Honoraria. Davids:Surface Oncology: Research Funding; Roche: Consultancy; Sunesis: Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy; Sunesis: Membership on an entity's Board of Directors or advisory committees; Verastem: Consultancy, Research Funding; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Surface Oncology: Research Funding; Astra-Zeneca: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Gilead: Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Roche: Consultancy; MEI Pharma: Consultancy, Research Funding; Astra-Zeneca: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Verastem: Consultancy, Research Funding; Roche: Consultancy; Sunesis: Membership on an entity's Board of Directors or advisory committees; Genentech: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Genentech: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Research Funding; BMS: Research Funding; MEI Pharma: Consultancy, Research Funding; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Genentech: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pharmacyclics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; TG Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding; TG Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pharmacyclics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; TG Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Merck: Consultancy; Merck: Consultancy; Celgene: Consultancy; Astra-Zeneca: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Gilead: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Merck: Consultancy; Celgene: Consultancy; BMS: Research Funding; Surface Oncology: Research Funding; MEI Pharma: Consultancy, Research Funding; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Verastem: Consultancy, Research Funding.

Abstract Introduction: Given the established role of PD-1 in mediating immune suppression in chronic lymphocytic leukemia (CLL), we tested and reported the efficacy of PD-1 blocking antibody pembrolizumab in relapsed and transformed CLL patients. A selective response of pembrolizumab (~40%) in patients with RT, particularly after prior ibrutinib, was observed (Ding, Blood, 129:3419). Correlative analysis showed PD-1 expression in tumor B-cells of patients with RT and aggressive CLL after progression on ibrutinib. PD-1, an inhibitory receptor expressed on CLL T-cells, inhibits the immune synapse and cytotoxic T cell functions via the interactions with its ligands. However, the expression pattern and role of PD-1 in tumor B-cells is not well defined. In this study we investigated the functional implication of the PD-1 signaling axis in B-cell pathobiology in CLL and RT patients. Methods: 26 CLL-involved lymph node (LN) and 20 RT-involved LN were tested for PD-1 expression by immunohistochemistry (mouse clone NAT105, Abcam). For in vitro study, we checked PD-1 expression in 11 lymphoma cell lines and 1 CLL cell line by both flow cytometry and Western blot (WB) analysis. Effect of PD-1 knockdown using CRISPR/Cas9 system (Addgene) and over-expression of PD-1 using pLEX-lentiviral (Thermoscientific) or pRetro-retroviral (Clonetech) system were evaluated on pro-survival and apoptotic signaling pathways by Western blot analysis. Gene expression signatures in CLL and RT patients were also evaluated by Illumina-based RNA sequencing using FFPE-nodal tissue obtained by clinical biopsy (Tempus Labs; Chicago, IL). Results: The expression of PD-1 was significantly increased in RT-LN compared to CLL-LN. (mean ± SEM in RT vs. CLL, 30.6 ± 4.7 vs. 11.5 ± 2.8, p < 0.001). PD-1 expression was highest in patients with RT where the immediate prior CLL therapy was ibrutinib (Figure 1A). Among all cell lines tested for PD-1 expression, the expression of PD-1 by WB and flow was highest in Mino (mantle cell lymphoma line), followed by moderate expression in Jvm2 (B-PLL line) and Mec1 (CLL line), and very low-level expression in both Jeko-1 (B-NHL line) and lymphoma line 'Karpas299'. CRISPR/Cas9 mediated depletion of PD-1 in Mino cells inhibited constitutively active Akt, p70S6K and mTOR pathway, accompanied by significant downregulation of the anti-apoptotic proteins, Bcl-2, Mcl-1 and XIAP, but P-ERK1/2 was not affected. Constitutive lentiviral (pLEX-PD-1)-mediated overexpression of PD-1 in Jeko-1 and doxycycline regulated inducible retroviral (pRetro-PD-1) mediated overexpression of PD-1 in Karpas299 activated Akt, mTOR and p70S6K pathway. Overexpression of PD-1 in Jeko-1 significantly increased Bcl-2 and Mcl-1 and in Karpas299 increased Bcl-2, Mcl-1 and XIAP expression (Figure 1B). A parallel genetic analysis using RNA sequencing was performed on 5 nodal tissues involved by either RT or progressive CLL after these patients developed clinical progression after prior ibrutinib therapy. In all 5 patients, overexpression of PD-1 was associated with increased expression of Bcl-2 and mTOR regardless of the genetic mutations detected (including TP53, ATM, BTK, NOTCH1, XPO1, SF3B1, TET2 etc). However, in 2 patients who received prior chemoimmunotherapy, similar overexpression of gene signature was not observed by RNA sequencing analysis, alternative pathways including Met or NFkB overexpression was detected. Given these clinical and laboratory findings, we have treated 2 RT patients with a combination of BTK and Bcl-2 inhibitors (ibrutinib and venetoclax, respectively) whose CLL transformed after prior ibrutinib. Significant reduction of tumor burden was observed in both cases with one complete response and one mixed response. Conclusion: An increased expression of PD-1, Akt/mTOR and Bcl-2 gene signature was first observed in RT patients after prior ibrutinib therapy. PD-1 overexpression in the tumor B-cells of RT and progressive CLL patients likely regulate AKT/mtOR to upregulate Bcl-2. Targeting both BTK and Bcl-2 pathways in addition to PD-1 blockade appear to be a promising strategy to treat these aggressive diseases. Disclosures Parikh: Gilead: Honoraria; Janssen: Research Funding; Abbvie: Honoraria, Research Funding; Pharmacyclics: Honoraria, Research Funding; MorphoSys: Research Funding; AstraZeneca: Honoraria, Research Funding. Kenderian:Novartis: Patents & Royalties; Tolero Pharmaceuticals: Research Funding; Humanigen: Research Funding. Ansell:Takeda: Research Funding; Trillium: Research Funding; Affimed: Research Funding; Celldex: Research Funding; Merck & Co: Research Funding; Regeneron: Research Funding; LAM Therapeutics: Research Funding; Bristol-Myers Squibb: Research Funding; Seattle Genetics: Research Funding; Pfizer: Research Funding. Kay:Infinity Pharm: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Acerta: Research Funding; Agios Pharm: Membership on an entity's Board of Directors or advisory committees; Cytomx Therapeutics: Membership on an entity's Board of Directors or advisory committees; Tolero Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Gilead: Membership on an entity's Board of Directors or advisory committees; Morpho-sys: Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees. Ding:Merck: Research Funding.

Abstract Peripheral immune dysfunction in B-Chronic Lymphocytic Leukemia (CLL) is well-studied and likely relates to the incidence of serious recurrent infections and second malignancies that plague CLL patients. However, the current paradigms of known immune abnormalities are not able to consistently explain these complications and it is not easy to correct CLL patient immune status. Here, we expand on our preliminary reports that demonstrate bone marrow (BM) hematopoietic dysfunction in early and late stage untreated CLL patients. We found reduced short-term functional capacity of hematopoietic progenitors in BM using colony forming unit assays (Figure 1A-C) and flow cytometry revealed significant reductions in frequencies of hematopoietic stem and progenitor cell (HSPC) populations (exemplified by Lin-CD34+ HSPCs, Figure 1D). We further report that protein levels of the transcriptional regulators HIF-1α, GATA-1, PU.1, and GATA-2 are overexpressed in distinct HSPC subsets from CLL patient BM, providing molecular insight into the basis of HSPC dysfunction. Interestingly, sustained myelopoiesis, evaluated by limiting dilution analysis in long-term culture-initiating cell (LTC-IC) assays maintained for five weeks, revealed no difference between healthy controls and CLL patients. These new data indicate that when HSPCs are removed from the leukemic microenvironment for ample in vitro culture time, they recover the ability to sustain myelopoiesis. To further assess the impact of the CLL microenvironment on HSPC biology, isolated HSPCs (CD34+ BM cells) from healthy controls were exposed in vitro to known leukemic microenvironment constituents. Exposure to TNFα, a cytokine constitutively produced by CLL B cells, resulted in rapid increases in PU.1 and GATA-2 proteins (Figure 2A-D). Similarly, addition of TNFα to the LTC-IC assay resulted in a striking ablation of myelopoiesis, even at the highest input cell concentration. Further, overexpression of PU.1 and GATA-2 were observed in HSPCs following co-culture with CLL B cells, a result that was not recapitulated when cells were exposed to IL-10, another cytokine constitutively produced by CLL B cells. These findings indicate specific components of the leukemic microenvironment are involved in HSPC modulation. Together, these findings expand on our previous observations of BM hematopoietic dysfunction in untreated CLL patients and offer new molecular insights into the contribution of the leukemic microenvironment on immunodeficiency in CLL. Disclosures Ding: Merck: Research Funding. Parikh:Pharmacyclics: Honoraria, Research Funding; MorphoSys: Research Funding; Janssen: Research Funding; Abbvie: Honoraria, Research Funding; Gilead: Honoraria; AstraZeneca: Honoraria, Research Funding. Kay:Morpho-sys: Membership on an entity's Board of Directors or advisory committees; Agios Pharm: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Acerta: Research Funding; Infinity Pharm: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Tolero Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Cytomx Therapeutics: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees, Research Funding.

Abstract Background Approximately 2-8% patients with chronic lymphocytic leukemia (CLL) will transform to diffuse large B-cell lymphoma (DLBCL, Richter syndrome [RS]). Clinical characteristics and molecular markers at the time of CLL diagnosis are associated with the risk of RS; however, there are no data regarding germline genetic variations and the risk of RS. Genomewide association studies (GWAS) have shown several single-nucleotide polymorphisms (SNPs) that are associated with a higher risk of familial CLL. It is not known whether any of these polymorphisms also predispose to RS. Methods Since 2002, all consecutive patients with newly diagnosed (<9 months diagnosis) CLL at Mayo Clinic were offered enrollment into a prospective genetic epidemiology study. Patients completed extensive epidemiologic questionnaires and baseline clinical, laboratory, and biologic data were abstracted using a standard protocol. Genotyping of germline tissue at diagnosis was performed using an Illumina iSelect panel and Affymetrix 6.0 SNP chip. All patients were prospectively and longitudinally followed at defined time-points with systematic collection of data on treatments, second cancers, and RS. All patients with biopsy-proven DLBCL during follow-up were considered to have undergone transformation into RS. Time to RS was calculated from CLL diagnosis date until RS or until last follow-up date for those with no RS. SNPs were modeled in two ways: ordinal and dominant. Cox regression was used to estimate hazard ratio (HR) for individual SNPs with time to transformation. Results Thirteen of the GWAS-discovered SNPs associated with risk of developing CLL were available and genotyped on 620 CLL patients. Median age at diagnosis of CLL was 62 years (range 27-88), and 428 (69%) were male. Three hundred and ten (51%) patients were low (0) Rai stage, 271 (45%) were intermediate (I-II) Rai stage, and 22 (4%) were advanced (III-IV) Rai stage. The immunoglobulin heavy chain gene was unmutated in 189 (40%) patients; 157 (32%) patients expressed ZAP-70, 163 (29%) expressed CD38 and 104 (31%) expressed CD49d. Fluorescence in-situ hybridization (FISH) revealed that 210 (41%) patients had del13q, 90 (18%) patients had trisomy 12, 37 (7%) had del11q, 23 (5%) had del17p and 141 (28%) had no detectable FISH abnormalities. As of last follow-up, 239 (39%) patients received therapy for CLL. After a median follow-up of 5.9 years (range 0-11), 15 (2.4%) patients developed biopsy-proven RS. The median time to RS in these 15 patients was 4.5 years (range 1.0-8.7 years). The ordinal HR for the 13 SNPs tested, their corresponding genes, and p-values are shown in Table 1. Germline polymorphisms in a single SNP, rs4987852, encoding for BCL2 (chromosome 18), was significantly associated with an increased risk of RS (ordinal HR=3.9; 95% CI=1.6-9.8; p-value=0.004). This allele was present in 48/605 (8%) non-transformed CLL patients compared to 4/15 (27%) of patients with RS. Time to RS according to the Kaplan-Meier analysis for rs4987852 is shown in Figure 1. This SNP is located in a region in which t(14;18) translocation breakpoints commonly occur in follicular lymphoma and overexpression of BCL2 leads to an increased incidence of B-cell lymphomas in mice. Conclusion Our results suggest that inherited genetic polymorphisms predispose CLL patients to develop RS. Specifically, SNP (rs4987852) present on the BCL2 gene on chromosome 18 in CLL is associated with an increased risk of transformation to RS. These observations require replication in other CLL cohorts. Disclosures: Shanafelt: Genentech: Research Funding; Glaxo-Smith-Kline: Research Funding; Cephalon: Research Funding; Hospira: Research Funding; Celgene: Research Funding; Polyphenon E International: Research Funding.

Abstract Clonal hematopoiesis of indeterminate potential (CHIP) is defined as somatic mutations in clonal blood cells of individuals without any other hematological abnormalities and have been identified using whole exome sequencing (WES) from pre-specified genes. CHIP is reportedly associated with aging, reduced overall survival, cardiovascular disease, and hematologic disease, mainly myeloid cancers. Additionally, whole genome sequencing and WES studies in CLL cases have identified putative CLL driver genes with recurrent somatic variants or copy number alterations. Here, we investigate the associations of CHIP and mutations in CLL somatic driver genes with risk of CLL and MBL, a precursor to CLL. Using WES, 571 individuals from 132 CLL families were sequenced from two different sites, Mayo Clinic (92 families) and National Cancer Institute (NCI, 40 families), including 251 CLLs, 74 MBLs, and 246 unaffected relatives. DNA was extracted from buccal cells (Mayo Clinic) and peripheral blood (NCI). Allele counts from gVCF files were extracted for specific genes and analyzed. Variants were annotated using the Variant Effect Predictor in Ensembl, genome build GRCh37 (http://useast.ensembl.org/index.html). Highly-sensitive flow cytometry of the blood was used to screen for MBL. CHIP was defined as in Genovese et al., 2014 as the presence of any of the following: A) disruptive mutations in ASXL1, TET2, or PPM1D; B) missense mutation p.617F in JAK2; C) disruptive or missense mutations in DNMT3Alocalized to exons 7 to 23D) any mutations reported at least 7 times in hematological malignancies in the Catalogue of Somatic Mutations in Cancer (COSMIC); and (E) No variant allelic fraction (VAF) threshold. CLL driver genes included disruptive or missense mutations in ATM, BIRC3, MYD88, NOTCH1, SF3B1, TP53, EGR2, POT1, NFKBIE, XPO1, or FBXW7with VAF greater than 0.1. Mutations from COSMIC and CLL driver genes were excluded if the minor allele frequency in 1000 Genomes was greater than 0.5%. Data was analyzed using logistic regression adjusting for age, sex, and site. Odds ratios (OR) and 95% confidence intervals (CI) were estimated. Median age for CLL, MBL, and unaffected was 63, 61.5, and 54, respectively. The unaffected relatives were significantly younger than both the CLL and MBL groups (p<0.0001), with no difference between CLL and MBL (p=0.46). A total of 70 (12%) individuals from 54 different families had CHIP. CHIP was characterized in the majority of samples as mutations in DNMT3A, ASXL1, and TET2with 43, 9 and 8 individuals, respectively. As expected, CHIP was associated with age (p<0.001) but not sex (p=0.87). CHIP was present in 42 (17%) CLLs, 9 (12%) MBLs, and 19 (8%) unaffected relatives. There was a significant association between the presence of CHIP and CLL risk compared to unaffected relatives (OR= 2.19, 95% CI: 1.20 - 4.13, p=0.013) but not with MBL risk (OR=1.34, 95% CI: 0.54 - 3.11, p=0.51). Using the CLL driver genes, we found mutations in 119 (47%) CLL, 20 (27%) MBL, and 70 (29%) unaffected relatives. Mutations in CLL driver genes were associated with CLL risk compared to unaffected relatives (OR = 2.51, 95% CI: 1.64 - 3.87, p<0.0001), but there was no evidence for increased MBL risk (OR = 1.00). These results held when we subset the analysis to the Mayo only data where the DNA was extracted from buccal cells. This study further supports the association between mutations in CHIP related genes and risk of hematologic malignancies, in particular CLL. This is the first report of the prevalence of CHIP in MBLs. Although MBL and CHIP represent clonal population of blood cells, our data suggest the clones are different. Mutations in CLL driver genes are also associated with CLL risk but show little to no evidence with increased MBL risk. Interestingly, our unaffected relatives of CLL cases also had a high frequency of CLL driver mutations. Future studies are needed to understand these acquired mutations (both in CHIP- and CLL driver- related genes) in the unaffected to MBL to CLL continuum. Disclosures Parikh: Abbvie: Honoraria, Research Funding; Pharmacyclics: Honoraria, Research Funding; MorphoSys: Research Funding; AstraZeneca: Honoraria, Research Funding; Gilead: Honoraria; Janssen: Research Funding. Ding:Merck: Research Funding. Cerhan:Jannsen: Other: Scientific Advisory Board; Celgene: Research Funding; Nanostring: Research Funding. Shanafelt:Jansen: Research Funding; Pharmacyclics: Research Funding; Genentech: Research Funding; GlaxoSmithKline: Research Funding. Kay:Morpho-sys: Membership on an entity's Board of Directors or advisory committees; Infinity Pharm: Membership on an entity's Board of Directors or advisory committees; Cytomx Therapeutics: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Agios Pharm: Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Acerta: Research Funding; Tolero Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Gilead: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees.

Abstract Background MBL is a precursor state to CLL, with a prevalence of ~5-8% in the general population and 15-18% in CLL families. To date, 41 single nucleotide polymorphisms (SNPs) have been found to be associated with CLL. We previously showed that a PRS of the weighted average of the number of risk alleles of these SNPs is associated with CLL risk using cases and controls from the International Lymphoma Epidemiology (InterLymph) Consortium. We validated this score in an independent sample of CLL cases and controls from the Genetic Epidemiology of CLL (GEC) Consortium, a cohort of families with ≥2 members with CLL. In the CLL families we also reported an association between the PRS and MBL risk, where 93% of MBLs were low-count MBL. Here we evaluate the PRS in an independent sample ascertained from the Mayo Clinic Biobank. Methods The Mayo Clinic Biobank is a large-scale bio-repository of adult patients assembled to provide a wide array of health-related research studies. Biobank participants (N=2530) were screened for MBL using a highly-sensitive, 8-color (CD38, CD45, Kappa, Lambda, CD19, CD23, CD5 and CD20) flow-cytometry assay on stored cryopreserved peripheral blood mononucleotide cells. Low-count and high-count MBL were defined as those individuals who had <85% and ≥85 clonal B-cells out of total B-cells, respectively. Individuals without MBL ("controls") were frequency matched to MBLs based on age and sex, after excluding non-Caucasian and non-interpretable flow results. Participants were genotyped using the Illumina OmniExpress array. Standard genotyping quality-control metrics were applied. We computed the PRS as previously published and categorized it by quintiles based on values previously used with InterLymph controls. The middle quintile served as the reference category. We used logistic regression to estimate odds ratios (ORs) and 95% confidence intervals (CI), adjusting for age at consent, sex, and socioeconomic status. In addition, we compared the median PRS by low-count MBL and high count MBL using the Mann-Whitney U test. Results We identified 276 MBLs overall and 2109 controls; 97% (N=267) of MBLs had low-count MBL and only 3% (N=9) had high-count MBL. We then selected 844 controls frequency matched to the MBL cases on age and sex. Family history of leukemia/lymphoma was 11.3% among MBLs overall and 8.8% among controls. The median PRS was 7.88 and 7.46 (Figure) among MBLs overall and controls, respectively. The continuous PRS had a 1.75-fold increased risk for MBL overall (CI:1.5-2.1, P=2.65x10-12). Compared to the middle quintile, the highest quintile had 2.2-fold increased risk for MBL overall (CI:1.5-3.3, P=1.46x10-4) and the lowest quintile had 0.6-fold decreased risk (CI:0.4-0.96, P=0.03). The median PRS for low-count and high count MBL were 7.86 and 8.04, respectively. The continuous PRS had a 1.75-fold increased risk for low-count MBL (CI:1.5-2.1, P=4.81x10-12) and a 1.89-fold increased risk for high-count MBL (CI:0.8-4.2, P=0.13), however, the effect is not statistically significant between high-count and low-count MBL (P=0.89). Conclusion In this independent sample, we validated our previous findings that the CLL PRS is associated with MBL risk. Although the sample size of high-count MBL was limited (N=9), there is evidence of a weak trend towards a higher PRS compared to low-count MBL and controls Larger sample size of high-count MBL is warranted in order to stratify MBL risk by low-count and high-count MBL. These results may help identify individuals at higher risk of MBL including low-count and high-count MBL, beyond the risk associated with age and family history of CLL. Figure: Polygenic risk score distribution by control and MBL status Figure. Figure. Disclosures Parikh: Janssen: Research Funding; Pharmacyclics: Honoraria, Research Funding; Gilead: Honoraria; Abbvie: Honoraria, Research Funding; AstraZeneca: Honoraria, Research Funding; MorphoSys: Research Funding. Cerhan:Nanostring: Research Funding; Celgene: Research Funding; Jannsen: Other: Scientific Advisory Board. Kay:Janssen: Membership on an entity's Board of Directors or advisory committees; Acerta: Research Funding; Infinity Pharm: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Agios Pharm: Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Cytomx Therapeutics: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Tolero Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Morpho-sys: Membership on an entity's Board of Directors or advisory committees. Shanafelt:Genentech: Research Funding; Pharmacyclics: Research Funding; GlaxoSmithKline: Research Funding; Jansen: Research Funding.

Abstract Abstract 3850 Background: We have recently shown that primary myelofibrosis (PMF) was associated with increased plasma levels of IL-1b/IL-1RA/IL-2R/IL-6/IL-8/IL-10/IL-12/IL-13/IL-15/TNF-α/G-CSF/INF-α/MIP-1α/MIP-1b/HGF/IP-10/MIG/MCP-1/VEGF in PMF (J Clin Oncol 2011; 29: 1356). In addition, increased levels of IL-8, IL-2R, IL-12, IL-15 and IP-10 were independently associated with inferior survival. In the current study, we focused on the plasma cytokine profile in polycythemia vera (PV) and examined how it compares with PMF or in a cohort of PV patients whose samples were collected during follow-up. We also looked for phenotypic and prognostic correlates. Methods: Study inclusion for patients with PV required availability of archived plasma within one year of diagnosis. Samples from PV patients seen at different points post-diagnosis were also collected, in order to compare their cytokine profile with that of patients whose samples were collected within one year of diagnosis. Standard procedures were followed to centrifuge peripheral blood samples at 4°C and store aliquots at −80°C. Concentrations of 30 plasma cytokines/chemokines were analyzed in duplicates using Multiplex Bead-based Luminex Technology (Invitrogen, Carlsbad, CA, USA): IL-1β, IL-1RA, IL-2, IL-2R, IL-4, IL-5, IL-6, IL-7, IL-8, IL-10, IL-12, IL-13, IL-15, IL-17, EGF, eotaxin, FGF-b, GM-CSF, G-CSF, HGF, IFN-α, IFN-γ, IP-10, MCP-1, MIG, MIP-1α, MIP-1β, RANTES, TNF-α, and VEGF. Measurements were performed on a Luminex 200 analyzer (Luminex Corporation, Austin, TX, USA) and resulting data were evaluated using STarStation Software Version 2.3 (Luminex Corporation, Austin, TX, USA). Results I: Plasma cytokines in PV (n=36 for samples collected within one year of diagnosis and n=40 for samples collected beyond that time point) vs. PMF (n=92) vs. normal controls (n=35) There was no significant difference between the three groups in the plasma levels of the following cytokines: IL-1β, IL-2, IL-4, EGF, and IL-17. PV and normal controls had similar levels of IL-2R, IL-5, FGF-b, and TNF-α; all four cytokines were elevated in PMF. The levels of the following cytokines were equally increased in PV and PMF: IL-1RA, IL-7, HGF, MIG, and VEGF. The following cytokines were also elevated in both PMF and PV but predominantly so in PV (MIP-1α) or PMF (IL-6, IL-8, IL-12, IL-13, IL-15, MIP-1β, IP-10, and MCP-1). Eotaxin and GM-CSF were elevated in PV but not PMF. Compared to normal controls, significantly lower levels were noted for IL-10 in PV and IFN-α and IFN-γ for PMF. IFN-α and IFN-γ levels were both elevated in PV. Comparison of PV samples collected within one year of diagnosis (n =36) vs. those collected beyond that time point (n =40) showed significantly increased levels of IL-8 (p=0.0005) and borderline significant increases in IP-10 (p=0.09) and IL-2R (p=0.09). Results II: Clinical correlates of plasma cytokines in PV Among the above-listed cytokines that were abnormally increased or decreased in PV, significant correlations were seen with sex (IP-10 and GM-CSF), age (IP-10, eotaxin), platelet count (MIG), hemoglobin level (IL-6), arterial thrombosis (IFN-γ, IL-1RA, VEGF, MIP-1α), and abnormal karyotype (IL-13, MIP-1α). None of the cytokines correlated with leukocyte count, venous thrombosis, pruritus or microvascular symptoms. The following, treated as continuous variables, were associated with inferior survival: IL-7, HGF, IFN-α, MCP-1, GM-CSF and IL-10 (p<0.05 for all). The number of events and sample size were too small to perform multivariable analysis. Conclusions: Plasma cytokine levels in PV are markedly abnormal and show both similarities and differences with PMF; the similarities became more pronounced in patients whose samples were examined at later stages of their disease. The current study suggests prognostic implications that warrant validation in a larger number of patients. Disclosures: No relevant conflicts of interest to declare.

Abstract Background:Recurrent mutations in ATM, JAK1/3 and STAT5B genes have been identified in T-cell prolymphocytic leukemia (T-PLL), a mature T cell leukemia with poor survival. However, much remains to be understood regarding the dysregulated pathways involved in the pathogenesis of this aggressive disease. Here, we integrated the analyses of whole exome sequencing (WES) and transcriptomes of a cohort of 12 T-PLL samples to gain further insights into molecular mechanisms of this malignancy. Methods: Leukemic cells were isolated from peripheral blood or bone marrow samples of T-PLL patients. Tumor DNA and RNA, and germline DNA were extracted from purified leukemic T cells and bone marrow derived stromal cells, respectively. WES (n=12) and transcriptome analysis (n=10) were performed and data analyzed with published standard methods (Robinson et al. 2010 and DePristo et al. 2011) Results: 7 paired tumor and germline DNA and 5 tumor-only DNA samples were used for WES analysis. Mutations in ATM and TET2 were detected in 4 (33%) and 1 (8%) patients, respectively. JAK3 (p.M511I, p.Q501H and p.Q503H) or STAT5B (2 p.T628S and 1 p.N642H) mutations each occurred in 3 (25%) cases and were mutually exclusive, consistent with prior reports. Importantly, we found several novel mutations in genes with regulatory roles in the NOTCH signaling pathway. Specifically, 2 somatic mutations p.A3V and p.A3S in NOTCH2 and 2 other mutations (p.S244L and p.A1414V) in NOTCH4 were identified in 4 (33%) patients. One mutation was in the EGF- like and another one in the NODP domain critical for NOTCH-mediated cellular differentiation. Two (16.7%) novel missense mutations (p.G174D and p.V836I) were found in MAML2. Three missense mutations (2 p.S583N and 1 p.R190H) occurred in MAML1. Both MAML2 and MAML1 are essential cofactors of the NOTCH signaling pathway. In addition, a somatic mutation in the NOTCH signal regulator DTX2 (p.G268D) was detected. Altogether 7 (58.3%) patients harbored mutations in genes with a regulatory role in the NOTCH pathway. Among the epigenetic modifiers, we found deletions and point mutations in KDM6B and KDM6A in 4 (30%) patients including 2 codon deletions in KDM6B (p.X751Val) and 1 missense mutation each in KDM6B (p.R1016Q) and KDM6A (p.V510G). KDM6A and KDM6B are histone H3 lysine 27 demethylases known to be involved in regulation of DNA repair and play an important role in embryonic differentiation. Transcriptome analyses of 10 T-PLL cases versus normal CD3+ T cells from 5 healthy donors revealed 706 up-regulated and 655 down-regulated genes. Consistent with prior data, TCL1A and TCL1B were significantly overexpressed (23.7 and 13.1 fold, respectively). Using Ingenuity Pathway Analysis, we found PTEN Signaling, glutamate receptor, and axonal guidance signaling to be among the top 3 upregulated pathways. The top upstream regulators implicated for the up-regulated signals were FGF, Wnt/β-catenin and TNF. The top 3 down-regulated pathways were granulocyte adhesion and diapedesis, IL-17A in psoriasis and IL-10 signaling. The top regulators for the down-regulated pathways were LPS, TNF and IFNg. Wnt/β-catenin and Human embryonic stem cell pluripotency signaling were among the top 20 up-regulated pathways. Many genes involved in the regulation of Wnt signal pathway were included in the above pathways, including Wnt ligands (Wnt9A, Wnt4), transmembrane receptors (CDH1, LRP5, FZD6, FZD7, SMO), cytoplasmic factor (AXIN2), and nuclear factors (MYC, SOX12, SOX8, SOX18, CCND1). Summary: Our study identified recurrent mutations in the NOTCH signaling pathway as well as dysregulated embryonic developmental pathway, e.g. Wnt/NOTCH as newly implicated molecular mechanisms in T-PLL pathogenesis for further functional studies. Additionally, novel (KDM6A and KDM6B) and known mutations (ATM, TET2) in chromatin regulatory genes underscore the importance of epigenetic dysregulation in the tumorigenesis of T-PLL. Disclosures Parikh: Pharmacyclics: Honoraria, Research Funding. Mustjoki:Ariad: Research Funding; Bristol-Myers Squibb: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding; Novartis: Honoraria, Research Funding. Ding:Merck: Research Funding.

Abstract Background: High risk CLL patients treated with novel targeted therapies continue to experience disease progression (PD), and more than 50% of these PD patients evolve into Richter's syndrome (RS), (Maddocks, Jama Oncol 2015). Standard chemotherapy for large cell lymphoma has limited efficacy (median overall survival <12 months) in RS. Novel immunotherapy using a PD-1 antibody to block immune checkpoint signals to activate the cytotoxic T -cell has significant efficacy in relapsed Hodgkin lymphoma (Ansell, NEJM 2015). We conducted a phase 2 trial to test the safety and clinical efficacy of the anti-PD-1 antibody pembrolizumab in patients with relapsed/refractory CLL and relapsed low grade B non-Hodgkin lymphoma (B-NHL) (MC1485 trial). Methods: MC1485includes two arms: patients with relapsed/refractory CLL (including RS) and patients with relapsed B-NHL. The main end points of this study are safety and overall response rate. The first 6 patients enrolled in either arm were included in a designed safety interim analysis. Here we report the initial interim analysis from the CLL arm. Relapsed/refractory CLL including RS who had ECOG performance 0-2 and normal organ function were included. Patients with active autoimmune disease or interstitial lung disease were excluded. Pembrolizumab 200 mg was administered intravenously every 3 weeks until progression, excessive toxicity, or completion of 2 years of therapy. Soluble plasma PD-L1 levels were measured in these 6 patients using an established ELISA assay (Frigola, Clin Cancer Res, 2011). CD8+ T cell subsets were assessed for their functional status using an established analysis (Liu, Oncoimmunology. 2013) at baseline and after 2 cycles of therapies. Results: As of July 27th, 2015, 16 relapsed/refractory CLL patients including 5 RS patients were enrolled. The median age was 71 years (58-81). The median number of prior therapies was 3 (1-6). All CLL patients had received chemoimmunotherapy (FCR/PCR). 4 out of 5 RS patients had received anthracycline-containing chemotherapy. 5 out of 8 patients who had received prior ibrutinib therapy progressed on ibrutinib. 8 patients had 17p-/TP53 mutation. Herein, we report preliminary results from the interim analysis of CLL arm including 4 RS and 2 CLL as well as the 5th RS who had response evaluation by PET. The median cycles of therapy administered was 4 (3-7). One patient experienced grade 2 cytokine release syndrome with transient febrile neutropenia, grade 3 headache and skin rashes. These symptoms resolved with steroid therapy. One patient experienced grade 3 myalgia and was also treated with steroids. The other patients in this safety cohort tolerated pembrolizumab well. The most common drug-related adverse events were grade 1 dyspnea (33%, 2/6) and grade 1 anemia (33%, 2/6). Based on investigator assessment using the Cheson 2007 International Working Group Criteria, 4 out of 5 RS patients had responded to therapy. One patient had a complete remission after 2 cycles and remains in remission. One patient had almost complete PET response after two cycles and is classified as PR as her bone marrow have not been re-evaluated yet. Two patients had notable responses with nodal and skin lymphoma improvements before they showed potential evidence of progressive diseases. The remaining 1 RS and 2 CLL had stable disease and continued on therapy at the last follow-up. Soluble PD-L1 levels (sPD-L1, n=6) were measured at baseline and after 2 cycles of therapies. 3 RS patients who had responded to therapy had decreased or stable sPD-L1 levels. The 4th RS and two CLL had increased sPD-L1 levels and had not demonstrated clinical response. CD8 T-cell subset analyses performed blindly (n=4) showed increased CD8 T cell function in one of the 4 patients tested. This patient who demonstrated CD8 T cell functional enhancement is the only patient in the 4 tested patients who had notable response to pembrolizumab. Conclusion: Pembrolizumab is tolerated in relapsed CLL and RS patients. Early efficacy observed in heavily pretreated RS patients including patients progressed on both anthracycline-based treatment and ibrutinib indicate PD-1 inhibition is a promising novel approach in patients with RS. Our CD8 T cell subset analysis may be used as a biomarker assay to predict clinical response in the era of novel immunotherapy. This trial and further correlative analysis is ongoing and will be presented at the ASH meeting. Disclosures Ding: Merek: Research Funding. Shanafelt:Cephalon: Research Funding; Pharmactckucs: Research Funding; Janssen: Research Funding; Hospira: Research Funding; Polyphenon E Int'l: Research Funding; Celgene: Research Funding; Glaxo-Smith_Kline: Research Funding; Genentech: Research Funding. Kay:Tolero Pharma: Research Funding; Hospira: Research Funding; Pharmacyclics: Research Funding; Genentech: Research Funding; Celgene Corporation: Membership on an entity's Board of Directors or advisory committees, Research Funding; Gilead: Membership on an entity's Board of Directors or advisory committees, Research Funding. Ansell:Bristol-Myers Squibb: Research Funding; Celldex: Research Funding.

Abstract Introduction: Ibrutinib has shown remarkable safety and efficacy in CLL. Due to CYP3A4 (3A4) metabolism, the concurrent use of 3A4 inhibitors/inducers with ibrutinib should be avoided. Ibrutinib is also associated with bleeding complications, in part due to effects on collagen-mediated platelet aggregation, thus caution is advised with the simultaneous use of anticoagulant (AC) and antiplatelet agents. It is unknown what proportion of CLL patients starting ibrutinib therapy in routine practice are on these medications. We conducted a retrospective study to evaluate these aspects in a large cohort of CLL pts treated with ibrutinib outside the context of clinical trials. Methods: Following IRB approval, consecutive CLL pts who initiated ibrutinib off-protocol at Mayo Clinic, Rochester, MN from November 2013 through July 2015 were evaluated. A medication review for drug-drug interactions was performed by a pharmacist on all pts. Baseline characteristics, concomitant medications, and toxicity were recorded. Time to toxicity and ibrutinib discontinuation were analyzed by Kaplan Meier and cumulative incidence methods accounting for competing risk of death, respectively. Results: Ninety-six CLL pts started ibrutinib. Median age was 66 years and 64 (67%) were male. Ibrutinib indications included: relapsed/refractory CLL (n=84), treatment-naïve CLL with del17p (n=8), and CLL with Richter's transformation (n=4). Approximately 80% had unmutated IGHV and 45% had del17p or del11q on FISH. Upon initial pharmacy consult prior to ibrutinib, the median number of concomitant medications was 9 (range, 1-31). Sixty (63%) pts were taking concurrent medications increasing their risk of ibrutinib toxicity and 4 (4%) pts were on drugs potentially reducing ibrutinib efficacy. At ibrutinib initiation, 16 (17%) pts were on concomitant 3A4 inhibitors. This included 9 (9%) on moderate 3A4 inhibitors (fluconazole, diltiazem, imatinib, cyclosporine) and 7 (7%) on strong 3A4 inhibitors (voriconazole, posaconazole, clarithromycin, itraconazole). In 4 pts, the 3A4 inhibitor was switched to another agent or discontinued to allow standard 420 mg daily dosing. Ibrutinib was initiated at 140 mg daily in 7 pts on moderate 3A4 inhibitors and at 140 mg every 48 hours in 5 pts on strong 3A4 inhibitors. Four (4%) pts were on strong 3A4 inducers (carbamazepine, rifampin, rifabutin) at the initiation of ibrutinib. The 3A4 inducer was discontinued prior to ibrutinib start in 3 pts, while the initial ibrutinib dose was decreased to 140 mg every 48 hours in the remaining patient (also on 2 strong 3A4 inhibitors). During the course of ibrutinib, an additional 8 (8%) pts were started on 3A4 inhibitors/inducers which necessitated dose modifications. Upon commencing ibrutinib, 9 (9%) pts were on concomitant AC (6 warfarin, 3 enoxaparin). Due to significant bleeding risk, warfarin was switched to enoxaparin in 2 pts, to aspirin (ASA) in 1 and warfarin was discontinued in 1. In 2 pts, an alternative AC could not be used so ibrutinib was begun at 140 mg daily and titrated upward. Twenty-nine (30%) pts were on ASA (3 [3%] also on clopidogrel) at ibrutinib initiation. Nineteen (20%) pts were on selective serotonin release inhibitors (SSRIs), and 9 (9%) were on NSAIDs. Thirteen (13%) pts were on fish oil and 24 (25%) were on herbal medications; all of which were discontinued prior to starting ibrutinib. Ten (10%) pts had clinically significant bleeding on ibrutinib including 4 (4%) requiring hospitalization (1 subdural hematoma). Of these 4 pts, 1 was on enoxaparin, 2 were on a SSRI and 1 a NSAID. Six pts had minor bleeding necessitating a dose reduction of ibrutinib to 140-280 mg daily. After 16 months follow-up, the risk of bleeding was 21% (95% CI: 1-37%, Figure). After a median follow-up of 7.6 months, 73 (76%) pts remain on ibrutinib. There was no difference in rates of discontinuation of ibrutinib between patients who were on 3A4 inhibitors/inducers versus those who were not. Conclusion: In the "real-world" setting, 2 out of 3 CLL patients commencing ibrutinib therapy is on a concomitant medication with a potentially clinically significant drug-drug interaction with ibrutinib. These findings have implications for the practicing hematologist who must maintain a high degree of vigilance when prescribing ibrutinib to CLL pts. We highly recommend a formal medication review by a clinical pharmacist in all patients initiating ibrutinib. Figure 1. Figure 1. Disclosures Ding: Merck: Research Funding. Kay:Hospira: Research Funding; Tolero Pharma: Research Funding; Genentech: Research Funding; Celgene Corporation: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pharmacyclics: Research Funding; Gilead: Membership on an entity's Board of Directors or advisory committees, Research Funding. Shanafelt:Glaxo-Smith_Kline: Research Funding; Pharmactckucs: Research Funding; Celgene: Research Funding; Genentech: Research Funding; Cephalon: Research Funding; Janssen: Research Funding; Hospira: Research Funding; Polyphenon E Int'l: Research Funding.