Use of anticoagulants and antiplatelet in patients with chronic lymphocytic leukaemia treated with single-agent ibrutinib

Bleeding events have been observed among a subgroup of chronic lymphocytic leukaemia (CLL) patients treated with ibrutinib. We analysed data from two studies of single‐agent ibrutinib to better characterize bleeding events and pattern of anticoagulation and antiplatelet use. Among 327 ibrutinib‐treated patients, concomitant anticoagulation (11%) or antiplatelet use (34%) was common, but major bleeding was infrequent (2%). Bleeding events were primarily grade 1, and infrequently (1%) led to discontinuation. Among 175 patients receiving concomitant anticoagulant or antiplatelet agents, 5 had major bleeding events (3%). These events were typically observed in conjunction with other factors, such as coexisting medical conditions and/or concurrent medications.

Long-term outcomes for patients with chronic lymphocytic leukemia who discontinue ibrutinib

BACKGROUND

Ibrutinib is a Bruton tyrosine kinase inhibitor and is approved for the treatment of patients with chronic lymphocytic leukemia (CLL) in frontline and relapsed/refractory settings. The authors previously reported poor outcomes for patients who discontinued ibrutinib; however, long-term outcomes were not reported.

METHODS

Data from 320 patients who received ibrutinib on clinical studies between 2010 and 2015 at The University of Texas MD Anderson Cancer Center were retrospectively analyzed.

RESULTS

Long-term outcomes among patients with CLL after they discontinued ibrutinib were analyzed. Ninety of 320 patients (28%) who were treated on ibrutinib-based regimens discontinued ibrutinib. Of these, 80 had relapsed/refractory disease, and 10 were treatment-naive. The median time to discontinuation was 15 months (range, 1.2-54 months). After a median follow-up of 38 months after starting ibrutinib, 40 patients (44%) remained alive. Major reasons for ibrutinib discontinuation were intolerance (n = 29; 32%), miscellaneous (n = 28; 31%), progression (n = 19; 21%), and Richter transformation (RT) (n = 9; 10%). The median survival according to the reason for discontinuation was 33 months for ibrutinib intolerance, 11 months for miscellaneous causes, 16 months for progressive CLL, and 2 months for RT. Among the 19 patients who had progressive CLL, 42% responded to subsequent therapy.

CONCLUSIONS

Ibrutinib discontinuation was observed during therapy. Patients with CLL who had disease transformation had especially poor outcomes, whereas those who developed progressive disease during ibrutinib therapy had a median survival of <1.5 years. Survival was associated with the reason for discontinuation; patients who had progressive CLL had better survival compared with those who had disease transformation. Effective salvage strategies for patients with CLL who progress on ibrutinib therapy is of critical importance. Cancer 2017;123:2268-2273. © 2017 American Cancer Society.

Leukemia cell proliferation and death in chronic lymphocytic leukemia patients on therapy with the BTK inhibitor ibrutinib

BACKGROUND. Ibrutinib is an effective targeted therapy for patients with chronic lymphocytic leukemia (CLL) that inhibits Bruton's tyrosine kinase (BTK), a kinase involved in B cell receptor signaling. METHODS. We used stable isotopic labeling with deuterated water (²H₂O) to measure directly the effects of ibrutinib on leukemia cell proliferation and death in 30 patients with CLL. RESULTS. The measured average CLL cell proliferation ("birth") rate before ibrutinib therapy was 0.39% of the clone per day (range 0.17%-1.04%); this decreased to 0.05% per day (range 0%-0.36%) with treatment. Death rates of blood CLL cells increased from 0.18% per day (average, range 0%-0.7%) prior to treatment to 1.5% per day (range 0%-3.0%) during ibrutinib therapy, and they were even higher in tissue compartments. CONCLUSIONS. This study provides the first direct in vivo measurements to our knowledge of ibrutinib's antileukemia actions, demonstrating profound and immediate inhibition of CLL cell proliferation and promotion of high rates of CLL cell death. TRIAL REGISTRATION. This trial was registered at clinicaltrials.gov (NCT01752426). FUNDING. This study was supported by a Cancer Center Support Grant (National Cancer Institute grant P30 CA016672), an NIH grant (CA081554) from the National Cancer Institute, MD Anderson's Moon Shots Program in CLL, and Pharmacyclics, an AbbVie company.

Ibrutinib Therapy Increases T Cell Repertoire Diversity in Patients with Chronic Lymphocytic Leukemia

The Bruton's tyrosine kinase inhibitor ibrutinib is a highly effective, new targeted therapy for chronic lymphocytic leukemia (CLL) that thwarts leukemia cell survival, growth, and tissue homing. The effects of ibrutinib treatment on the T cell compartment, which is clonally expanded and thought to support the growth of malignant B cells in CLL, are not fully characterized. Using next-generation sequencing technology, we characterized the diversity of TCRβ-chains in peripheral blood T cells from 15 CLL patients before and after 1 y of ibrutinib therapy. We noted elevated CD4⁺ and CD8⁺ T cell numbers and a restricted TCRβ repertoire in all pretreatment samples. After 1 y of ibrutinib therapy, elevated peripheral blood T cell numbers and T cell-related cytokine levels had normalized, and T cell repertoire diversity increased significantly. Dominant TCRβ clones in pretreatment samples declined or became undetectable, and the number of productive unique clones increased significantly during ibrutinib therapy, with the emergence of large numbers of low-frequency TCRβ clones. Importantly, broader TCR repertoire diversity was associated with clinical efficacy and lower rates of infections during ibrutinib therapy. These data demonstrate that ibrutinib therapy increases diversification of the T cell compartment in CLL patients, which contributes to cellular immune reconstitution.

Extended Treatment with Single-Agent Ibrutinib at the 420 mg Dose Leads to Durable Responses in Chronic Lymphocytic Leukemia/Small Lymphocytic Lymphoma

Purpose: Ibrutinib, a first-in-class, once-daily, oral inhibitor of Bruton tyrosine kinase, promotes apoptosis, and inhibits B-cell proliferation, adhesion, and migration. Ibrutinib has demonstrated single-agent efficacy and acceptable tolerability at doses of 420 and 840 mg in patients with chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) who were treatment-naïve (TN) or had relapsed/refractory (R/R) CLL after ≥1 prior therapy in a phase Ib/II study (PCYC-1102). Subsequently, the ibrutinib 420 mg dose was approved in CLL.Experimental Design: We report data with 44 months of follow-up on 94 patients with TN and R/R CLL/SLL receiving ibrutinib 420 mg once-daily in PCYC-1102 and the long-term extension study PCYC-1103.Results: Ninety-four CLL/SLL patients (27 TN, 67 R/R) were treated with ibrutinib (420 mg/day). Patients with R/R disease had received a median of four prior therapies (range, 1-12). Responses were rapid and durable and median duration of response was not reached. Best overall response was 91% [85% TN (complete response, CR 26%) and 94% R/R (9% CR)]. Median progression-free survival (PFS) was not reached in either group. The 30-month PFS rate was 96% and 76% for TN and R/R patients, respectively. Ibrutinib was well tolerated with extended follow-up; rates of grade ≥3 cytopenias and fatigue, as well as discontinuations due to toxicities decreased over time.Conclusions: Single-agent ibrutinib at 420 mg once-daily resulted in durable responses and was well tolerated with up to 44 months follow-up in patients with TN and R/R CLL/SLL. Currently, 66% of patients continue on ibrutinib. Clin Cancer Res; 23(5); 1149-55. ©2017 AACR.

Long-term Follow-up of Treatment with Ibrutinib and Rituximab in Patients with High-Risk Chronic Lymphocytic Leukemia

Background: Ibrutinib is an active therapy with an acceptable safety profile for patients with chronic lymphocytic leukemia (CLL), including high-risk patients with del17p or with TP53 mutations. Ibrutinib is broadly indicated for the treatment of patients with CLL and specifically including those with 17p deletion. The optimal use of ibrutinib in combination with other agents remains controversial.Experimental Design: We report the long-term outcome [median follow-up of 47 months (range, 36-51 months)] of 40 patients with high-risk CLL, treated on the first ibrutinib combination trial with rituximab (IR). The majority of patients (36/40) were previously treated.Results: Median age was 65 years, and 21 patients (52%) had 17p deletion. Median duration on treatment was 41 months (range, 2-51 months), and median number of treatment cycles was 42 (range, 2-49). Overall response rate was 95%, and 9 patients (23%) attained a complete remission. Twenty-one patients discontinued treatment, 10 due to disease progression, 9 for other causes, and 2 due to stem cell transplantation; the remaining 19 patients continue on ibrutinib. Median progression-free survival for all patients was 45 months, which was significantly shorter in the subgroup of patients with del17p (n = 21, 32.3 months, P = 0.02). Fourteen patients (35%) died, five from progressive disease, five from infections, and four from other causes. Median overall survival has not been reached.Conclusions: IR combination therapy leads to durable remissions in high-risk CLL; the possible benefit from the addition of rituximab is currently explored in a randomized trial. Clin Cancer Res; 23(9); 2154-8. ©2016 AACR.

Inhibition of demethylase KDM6B sensitizes diffuse large B-cell lymphoma to chemotherapeutic drugs

Histone methylation and demethylation regulate B-cell development, and their deregulation correlates with tumor chemoresistance in diffuse large B-cell lymphoma, limiting cure rates. Since histone methylation status correlates with disease aggressiveness and relapse, we investigated the therapeutic potential of inhibiting histone 3 Lys27 demethylase KDM6B, in vitro, using the small molecule inhibitor GSK-J4. KDM6B is overexpressed in the germinal center B-cell subtype of diffuse large B-cell lymphoma, and higher KDM6B levels are associated with worse survival in patients with diffuse large B-cell lymphoma treated with R-CHOP. GSK-J4-induced apoptosis was observed in five (SU-DHL-6, OCI-Ly1, Toledo, OCI-Ly8, SU-DHL-8) out of nine germinal center B-cell diffuse large B-cell lymphoma cell lines. Treatment with GSK-J4 predominantly resulted in downregulation of B-cell receptor signaling and BCL6. Cell lines expressing high BCL6 levels or CREBBP/EP300 mutations were sensitive to GSK-J4. Our results suggest that B-cell receptor-dependent downregulation of BCL6 is responsible for GSK-J4-induced cytotoxicity. Furthermore, GSK-J4-mediated inhibition of KDM6B sensitizes germinal center B-cell diffuse large B-cell lymphoma cells to chemotherapy agents that are currently utilized in treatment regimens for diffuse large B-cell lymphoma.

Functional Differences between IgM and IgD Signaling in Chronic Lymphocytic Leukemia

BCR signaling is a central pathogenetic pathway in chronic lymphocytic leukemia (CLL). Most CLL cells express BCRs of IgM and IgD isotypes, but the contribution of these isotypes to functional responses remains incompletely defined. We therefore investigated differences between IgM and IgD signaling in freshly isolated peripheral blood CLL cells and in CLL cells cultured with nurselike cells, a model that mimics the lymph node microenvironment. IgM signaling induced prolonged activation of ERK kinases and promoted CLL cell survival, CCL3 and CCL4 chemokine secretion, and downregulation of BCL6, the transcriptional repressor of CCL3 In contrast, IgD signaling induced activation of the cytoskeletal protein HS1, along with F-actin polymerization, which resulted in rapid receptor internalization and failure to support downstream responses, including CLL cell survival and chemokine secretion. IgM and IgD receptor downmodulation, HS1 and ERK activation, chemokine secretion, and BCL6 downregulation were also observed when CLL cells were cocultured with nurselike cells. The Bruton's tyrosine kinase inhibitor ibrutinib effectively inhibited both IgM and IgD isotype signaling. In conclusion, through a variety of functional readouts, we demonstrate very distinct outcomes of IgM and IgD isotype activation in CLL cells, providing novel insight into the regulation of BCR signaling in CLL.

Pre-BCR signaling in precursor B-cell acute lymphoblastic leukemia regulates PI3K/AKT, FOXO1 and MYC, and can be targeted by SYK inhibition

Precursor-B-cell receptor (pre-BCR) signaling and spleen tyrosine kinase (SYK) recently were introduced as therapeutic targets for patients with B-cell acute lymphoblastic leukemia (B-ALL), but the importance of this pathway in B-ALL subsets and mechanism of downstream signaling have not fully been elucidated. Here, we provide new detailed insight into the mechanism of pre-BCR signaling in B-ALL. We compared the effects of pharmacological and genetic disruption of pre-BCR signaling in vitro and in mouse models for B-ALL, demonstrating exquisite dependency of pre-BCR(+) B-ALL, but not other B-ALL subsets, on this signaling pathway. We demonstrate that SYK, PI3K/AKT, FOXO1 and MYC are important downstream mediators of pre-BCR signaling in B-ALL. Furthermore, we define a characteristic immune phenotype and gene expression signature of pre-BCR(+) ALL to distinguish them from other B-ALL subsets. These data provide comprehensive new insight into pre-BCR signaling in B-ALL and corroborate pre-BCR signaling and SYK as promising new therapeutic targets in pre-BCR(+) B-ALL.

Prognostic impact of persistent cytogenetic abnormalities at complete remission in adult patients with acute lymphoblastic leukemia

In acute myelogenous leukemia, the persistent detection of abnormal cytogenetics at complete remission (ACCR) is associated with inferior outcomes. However, the prognostic significance of ACCR in adult patients with acute lymphoblastic leukemia (ALL) is unknown. We evaluated 272 adult patients with ALL and abnormal cytogenetics at baseline who were treated with frontline induction chemotherapy, achieved complete remission (CR) and had cytogenetic analysis performed at the time of CR. ACCR was observed in 26 patients (9.6%). Median relapse-free survival was 22 months (95% CI, 12 months to not reached) for patients with ACCR vs. 48 months (range, 30-125 months) in patients with normal cytogenetics at CR (NCCR; P = 0.31). Median overall survival also did not differ significantly between the ACCR (99 months [range, 17 months to not reached]) and NCCR groups (67 months [range, 47 months to not reached], P = 0.86). The specificity of ACCR for minimal residual disease (MRD) positivity by multi-parameter flow cytometry (MFC) was 43%, and there was overall poor correlation between these two methods for the detection of residual disease. When patients were stratified by MRD status, the presence or absence of persistent cytogenetic abnormalities at CR did not add additional prognostic information. This study suggests that there is poor association between MRD assessment by MFC and the presence or absence of cytogenetic abnormalities at CR in adult patients with ALL. ACCR was not associated with adverse outcomes in ALL and did not add additional prognostic information when MRD status by MFC was known.

Chronic lymphocytic leukemia therapy: new targeted therapies on the way

INTRODUCTION

The critical role of the tissue microenvironment and B-cell receptor (BCR) signaling in chronic lymphocytic leukemia (CLL) pathogenesis, and the clinical success of targeted agents that disrupt BCR signaling are currently changing the CLL landscape. Three new drugs were recently approved for CLL therapy, and other agents are in late development.

AREAS COVERED

In this review, we summarize data on promising new targeted drugs for CLL. The heterogeneous mechanisms of actions of these molecules are described, such as the inhibition of BCR signaling, direct targeting of CD20 molecules on the CLL cell surface, and BCL-2 inhibition. We present preclinical and clinical data from phase I to III studies in order to describe efficacy and side effect profile of these new drugs. Data are derived from peer-reviewed articles indexed in PubMed and from abstracts presented at major international meetings.

EXPERT OPINION

Ibrutinib and idelalisib are challenging the role of chemo-immunotherapy in CLL therapy in the frontline and relapsed disease settings. High-risk CLL patients particularly benefit from these new agents. Venetoclax and obinutuzumab are other effective agents added to our therapeutic armamentarium. Studies to better define the optimal use of these drugs, alone, or rather in combination or sequenced are underway.

Clonal evolution in patients with chronic lymphocytic leukaemia developing resistance to BTK inhibition

Resistance to the Bruton's tyrosine kinase (BTK) inhibitor ibrutinib has been attributed solely to mutations in BTK and related pathway molecules. Using whole-exome and deep-targeted sequencing, we dissect evolution of ibrutinib resistance in serial samples from five chronic lymphocytic leukaemia patients. In two patients, we detect BTK-C481S mutation or multiple PLCG2 mutations. The other three patients exhibit an expansion of clones harbouring del(8p) with additional driver mutations (EP300, MLL2 and EIF2A), with one patient developing trans-differentiation into CD19-negative histiocytic sarcoma. Using droplet-microfluidic technology and growth kinetic analyses, we demonstrate the presence of ibrutinib-resistant subclones and estimate subclone size before treatment initiation. Haploinsufficiency of TRAIL-R, a consequence of del(8p), results in TRAIL insensitivity, which may contribute to ibrutinib resistance. These findings demonstrate that the ibrutinib therapy favours selection and expansion of rare subclones already present before ibrutinib treatment, and provide insight into the heterogeneity of genetic changes associated with ibrutinib resistance.

Outcomes of patients with chronic lymphocytic leukemia treated with first-line idelalisib plus rituximab after cessation of treatment for toxicity

BACKGROUND

More active therapies are needed for older and unfit patients with chronic lymphocytic leukemia (CLL) who are not eligible for chemoimmunotherapy with fludarabine, cyclophosphamide, and rituximab. The phosphyotidylinositol-3-kinase δ inhibitor idelalisib is effective in patients with treatment-naive and relapsed/refractory CLL as monotherapy and in combination with rituximab, but it can be associated with treatment-limiting adverse events, particularly diarrhea/colitis. The outcomes for patients who cease treatment for adverse events have not been previously described.

METHODS

The authors analyzed long-term follow-up data from 40 treatment-naïve patients aged ≥65 years who received treatment at The University of Texas MD Anderson Cancer Center on a phase 2 study of idelalisib plus rituximab for CLL.

RESULTS

In patients who permanently ceased treatment because of toxicity, the time to subsequent disease progression was analyzed according to baseline characteristics. Fifteen patients permanently ceased therapy (PCT) because of toxicity (PCTTOX ), most commonly diarrhea/colitis (n = 7), at a median of 11 months after commencing treatment. PCTTOX was associated with a higher risk of subsequent disease progression (hazard ratio, 6.61; 95% confidence interval, 1.77-16.15) relative to that observed in patients who remained on therapy. Ten patients subsequently progressed, and 7 required salvage therapy; 5 patients remained progression-free at a median of 23.3 months (range, 8.5-28.6 months). Patients who were positive for ζ-associated protein-70 had more rapid disease progression after treatment cessation (P = .048). There were no CLL-related deaths.

CONCLUSIONS

PCTTOX is the major determinant of PFS in patients who receive first-line idelalisib-based treatment. However, a subgroup of patients with favorable biologic characteristics has prolonged PFS, even after PCTTOX . The absence of CLL-related deaths indicates that salvage treatment is generally successful after PCTTOX . Cancer 2016;122:2505-11. © 2016 American Cancer Society.

Effects of pharmacological and genetic disruption of CXCR4 chemokine receptor function in B-cell acute lymphoblastic leukaemia

B cell acute lymphoblastic leukaemia (B-ALL) cells express high levels of CXCR4 chemokine receptors for homing and retention within the marrow microenvironment. Bone marrow stromal cells (BMSC) secrete CXCL12, the ligand for CXCR4, and protect B-ALL cells from cytotoxic drugs. Therefore, the therapeutic use of CXCR4 antagonists has been proposed to disrupt cross talk between B-ALL cells and the protective stroma. Because CXCR4 antagonists can have activating agonistic function, we compared the genetic and pharmacological deletion of CXCR4 in B-ALL cells, using CRISPR-Cas9 gene editing and CXCR4 antagonists that are in clinical use (plerixafor, BKT140). Both genetic and pharmacological CXCR4 inhibition significantly reduced B-ALL cell migration to CXCL12 gradients and beneath BMSC, and restored drug sensitivity to dexamethasone, vincristine and cyclophosphamide. NOD/SCID/IL-2rγnull mice injected with CXCR4 gene-deleted B-ALL cells had significant delay in disease progression and superior survival when compared to control mice injected with CXCR4 wild-type B-ALL cells. These findings indicate that anti-leukaemia activity of CXCR4 antagonists is primarily due to CXCR4 inhibition, rather than agonistic activity, and corroborate that CXCR4 is an important target to overcome stroma-mediated drug resistance in B-ALL.

Microenvironment interactions and B-cell receptor signaling in Chronic Lymphocytic Leukemia: Implications for disease pathogenesis and treatment

Chronic Lymphocytic Leukemia (CLL) is a malignancy of mature B lymphocytes which are highly dependent on interactions with the tissue microenvironment for their survival and proliferation. Critical components of the microenvironment are monocyte-derived nurselike cells (NLCs), mesenchymal stromal cells, T cells and NK cells, which communicate with CLL cells through a complex network of adhesion molecules, chemokine receptors, tumor necrosis factor (TNF) family members, and soluble factors. (Auto-) antigens and/or autonomous mechanisms activate the B-cell receptor (BCR) and its downstream signaling cascade in secondary lymphatic tissues, playing a central pathogenetic role in CLL. Novel small molecule inhibitors, including the Bruton's tyrosine kinase (BTK) inhibitor ibrutinib and the phosphoinositide-3-kinase delta (PI3Kδ) inhibitor idelalisib, target BCR signaling and have become the most successful new therapeutics in this disease. We here review the cellular and molecular characteristics of CLL cells, and discuss the cellular components and key pathways involved in the cross-talk with their microenvironment. We also highlight the relevant novel treatment strategies, focusing on immunomodulatory agents and BCR signaling inhibitors and how these treatments disrupt CLL-microenvironment interactions. This article is part of a Special Issue entitled: Tumor Microenvironment Regulation of Cancer Cell Survival, Metastasis, Inflammation, and Immune Surveillance edited by Peter Ruvolo and Gregg L. Semenza.

Ofatumumab and Lenalidomide for Patients with Relapsed or Refractory Chronic Lymphocytic Leukemia: Correlation between Responses and Immune Characteristics

PURPOSE

We evaluated efficacy and tolerability of the combination of ofatumumab and lenalidomide in patients with relapsed/refractory chronic lymphocytic leukemia (CLL), and explored whether immune system characteristics could influence the response to treatment.

EXPERIMENTAL DESIGN

Thirty-four patients were enrolled in this phase II study. Ofatumumab was administered at a dose of 300 mg on day 1, 1,000 mg on days 8, 15, and 22 during course 1, 1,000 mg on day 1 during courses 3-6, and once every other course during courses 7-24 (28-day courses). Oral lenalidomide (10 mg daily) was started on day 9 and continued for as long as a clinical benefit was observed.

RESULTS

The overall response rate was 71%. Eight patients (24%) achieved a complete remission (CR) or CR with incomplete recovery of blood counts, including 9% with minimal residual disease-negative CR. The median progression-free survival was 16 months, and the estimated 5-year survival was 53%. The most common treatment-related toxicity was neutropenia (grade >2 in 18% of the 574 patient courses). The most frequent infectious complications were pneumonia and neutropenic fever (24% and 9% of patients, respectively). We observed that patients who achieved a CR had at baseline higher numbers and a better preserved function of T cells and natural killer cells compared with non-responders.

CONCLUSIONS

The combination of ofatumumab and lenalidomide is a well-tolerated regimen that induces durable responses in the majority of patients with relapsed/refractory CLL. Our correlative data suggest a role of competent immune system in supporting the efficacy of this treatment. Clin Cancer Res; 22(10); 2359-67. ©2016 AACR.

B-cell receptor signaling in chronic lymphocytic leukemia and other B-cell malignancies

B-cell receptor (BCR) signaling has emerged as a key pathway for the expansion of neoplastic B-cell clones in several B-cell malignancies. The mechanisms that activate BCR signaling differ substantially among subtypes of B-cell lymphoma and leukemia. These include BCR stimulation by foreign or self-antigens, or the acquisition of mutations in components of the BCR pathway that result in autonomous or enhanced antigen-induced BCR signaling. Targeting BCR signaling with selective inhibitors of the BCR-associated kinases Bruton's tyrosine kinase, spleen tyrosine kinase, and phosphoinositide 3-kinase delta induces high response rates in patients with chronic lymphocytic leukemia, mantle cell lymphoma, Waldenström macroglobulinemia, and diffuse large B-cell lymphoma of the activated B-cell-like subtype and is currently transforming the therapeutic landscape in these diseases. Here we review the mechanisms of BCR activation that govern growth and survival of malignant B cells. We also summarize recent clinical trials of BCR inhibitors, with a focus on the most clinically advanced agents.

PI3K Signaling in Normal B Cells and Chronic Lymphocytic Leukemia (CLL)

B cells provide immunity to extracellular pathogens by secreting a diverse repertoire of antibodies with high affinity and specificity for exposed antigens. The B cell receptor (BCR) is a transmembrane antibody, which facilitates the clonal selection of B cells producing secreted antibodies of the same specificity. The diverse antibody repertoire is generated by V(D)J recombination of heavy and light chain genes, whereas affinity maturation is mediated by activation-induced cytidine deaminase (AID)-mediated mutagenesis. These processes, which are essential for the generation of adaptive humoral immunity, also render B cells susceptible to chromosomal rearrangements and point mutations that in some cases lead to cancer. In this chapter, we will review the central role of PI3K s in mediating signals from the B cell receptor that not only facilitate the development of functional B cell repertoire, but also support the growth and survival of neoplastic B cells, focusing on chronic lymphocytic leukemia (CLL) B cells. Perhaps because of the central role played by PI3K in BCR signaling, B cell leukemia and lymphomas are the first diseases for which a PI3K inhibitor has been approved for clinical use.