GM1 expression of non-Hodgkin's lymphoma determines susceptibility to rituximab treatment

Immunotherapy with rituximab alone or in conjunction with chemotherapy has significantly improved the treatment outcome of B-cell lymphoma patients. Nevertheless, a subpopulation of patients does not respond to rituximab. The reason for treatment failure as well as the exact mechanism of action is still uncertain. The function of rituximab has long been associated with the partitioning of CD20 molecules to lipid microdomains. We now show that the extent of CD20 recruitment to lipid rafts correlates with response to rituximab. In addition, expression of the raft-associated sphingolipid GM1 on lymphoma cells is associated with the susceptibility of lymphoma cells to rituximab. Furthermore, we show substantially different GM1 expression in various primary non-Hodgkin's lymphomas. Whereas chronic lymphocytic leukemia (CLL) cells have a low GM1 expression, marginal zone lymphoma cells exhibit much higher levels. Differences were not only detected among various lymphoma subgroups but also within one lymphoma subtype. Interestingly, whereas CLL cells from patients with high GM1 expression responded to rituximab, patients with low GM1 expressing CLL cells did not. These data show the importance of membrane microdomains in the effect of rituximab and may offer a predictive factor for the responsiveness of lymphoma cells to rituximab.     

Rituximab in Lymphoma and Chronic Lymphocytic Leukaemia: A Practice Guideline

Rituximab is the first monoclonal antibody to be approved for use by the US Food and Drug Administration in cancer. Its role in the treatment of non-Hodgkin lymphoma, including chronic lymphocytic leukaemia (CLL), has evolved significantly. We aimed to systematically review and update the literature on rituximab in lymphoma and CLL, and provide evidence-based consensus guidelines for its rational use. Validated methodology from the Cancer Care Ontario Program in Evidence-based Care was used. A comprehensive literature search was completed by a methodologist from the Hematology Disease Site Group of Cancer Care Ontario. Data were extracted from randomised controlled trials of rituximab-containing chemotherapy regimens for patients with lymphoma or CLL. Fifty-six primary randomised controlled trials were retrievable and met all inclusion criteria. Clinically important benefits in progression-free survival or overall survival were seen in the following settings: (i) addition of rituximab to combination chemotherapy for initial treatment of aggressive B-cell lymphomas, including diffuse large B-cell lymphoma, Burkitt lymphoma and HIV-related lymphoma with CD4 count ≥50/mm³; (ii) addition of rituximab to combination chemotherapy for initial and subsequent treatment of follicular lymphoma and other indolent B-cell lymphomas; (iii) use of rituximab maintenance in patients with indolent B-cell lymphomas who have responded to chemoimmunotherapy; (iv) addition of rituximab to fludarabine-based chemotherapy or chlorambucil for initial treatment of CLL. The consensus opinion of the Hematology Disease Site Group is that rituximab is recommended for these indications.     

Combined fludarabine and rituximab for low grade lymphoma and chronic lymphocytic leukemia

As both fludarabine and rituximab are active against indolent lymphoproliferative disorders, we have studied the combination of fludarabine and rituximab in patients with low-grade lymphoma and chronic lymphocytic leukemia (CLL) in phase I/II fashion. Of 33 patients enrolled, 21(63.6%) had low-grade lymphoma and 12 (36.4%) had CLL. They received fludarabine 30 mg/m 2 on days 1-4 and rituximab 125, 250 or 375 mg/m 2 on day 5 at intervals of 28 days to a maximum of 8 cycles. Three patients were removed from the study because of rituximab-associated anaphylaxis and four because of prolonged hematopoietic toxicity. Toxicity and responsiveness did not differ at the different dose levels of rituximab. For 29 evaluable patients, responses were seen in 82.8% and complete responses in 34.5%. Of 7 responding patients not referred for stem cell transplantation, 6 remain in complete remission at a median follow-up of 16 months (range 4-30 months). Of 13 previously untreated patients, all responded and 46.2% had a complete response. Of 16 previously treated patients, 68.5% responded and 25% had a complete response. The combination of fludarabine and rituximab has major activity and acceptable toxicity in patients with low-grade lymphoma and CLL.     

Single-agent rituximab as first-line and maintenance treatment for patients with chronic lymphocytic leukemia or small lymphocytic lymphoma: a phase II trial of the Minnie Pearl Cancer Research Network.

PURPOSE: To assess the efficacy and toxicity of first-line single-agent rituximab, followed by re-treatment with rituximab at 6-month intervals, in previously untreated patients with chronic lymphocytic leukemia (CLL) or small lymphocytic lymphoma (SLL). PATIENTS AND METHODS: Forty-four previously untreated patients with CLL/SLL received rituximab 375 mg/m2 weekly for 4 consecutive weeks. All patients were required to have one or more indications for treatment. Patients with objective response or stable disease continued to receive identical 4-week rituximab courses at 6-month intervals, for a total of four courses. RESULTS: The objective response rate after the first course of rituximab was 51% (4% complete responses). Twenty-eight patients received one or more additional courses of rituximab. At present, the overall response rate is 58%, with 9% complete responses. After a median follow-up of 20 months, the median progression-free survival (PFS) time was 18.6 months, and the 1- and 2-year PFS rates were 62% and 49%, respectively. Treatment was well tolerated, with only two episodes of grade 3 to 4 infusion-related toxicity. No cumulative toxicity or opportunistic infections occurred. CONCLUSION: Single-agent rituximab, used at a standard dose and schedule, is active in the first-line treatment of patients with CLL/SLL, producing substantially higher response rates than previously reported in relapsed or refractory patients (51% v 13%, respectively). Re-treatment with rituximab at 6-month intervals is well tolerated. The PFS time of 18.6 months in patients with CLL/SLL seems shorter than the 36- to 40-month median PFSs previously reported with first-line plus maintenance rituximab in patients with follicular lymphoma. Additional follow-up is required to fully assess the impact of this treatment strategy.     

Human CD59 inhibitor sensitizes rituximab-resistant lymphoma cells to complement-mediated cytolysis

Rituximab efficacy in cancer therapy depends in part on induction of complement-dependent cytotoxicity (CDC). Human CD59 (hCD59) is a key complement regulatory protein that restricts the formation of the membrane attack complex, thereby inhibiting induction of CDC. hCD59 is highly expressed in B-cell non-Hodgkin's lymphoma (NHL), and upregulation of hCD59 is an important determinant of the sensitivity of NHL cells to rituximab treatment. Here, we report that the potent hCD59 inhibitor rILYd4 enhances CDC in vitro and in vivo, thereby sensitizing rituximab-resistant lymphoma cells and primary chronic lymphocytic leukemia cells (CLL) to rituximab treatment. By defining pharmcokinetic/pharmacodynamic profiles of rILYd4 in mice, we showed that by itself rILYd4 does not adversely mediate in vivo hemolysis of hCD59-expressing erythrocytes. Increasing expression levels of the complement regulators CD59 and CD55 in rituximab-resistant cells occur due to selection of preexisting clones rather than de novo induction of these proteins. Moreover, lymphoma cells overexpressing CD59 were directly responsible for the resistance to rituximab-mediated CDC therapy. Our results rationalize the use of rILYd4 as a therapeutic adjuvant for rituximab treatment of rituximab-resistant lymphoma and CLL. Furthermore, they suggest that preemptive elimination of CD59-overexpressing subpopulations along with rituximab treatment may be a useful approach to ablate or conquer rituximab resistance.     

PI3K signaling pathway in normal B cells and indolent B-cell malignancies

In chronic lymphocytic leukemia (CLL) and non-Hodgkin lymphomas (NHLs), B-cell receptor signaling leads to activation of the phosphatidylinositol 3-kinase (PI3K) pathway. Idelalisib, a PI3Kδ inhibitor was approved in 2014 by the US Food and Drug Administration (FDA) in combination with rituximab for the treatment of patients with CLL for whom single-agent rituximab would be considered appropriate and as a single agent for patients with relapsed small lymphocytic lymphoma (SLL) and relapsed follicular lymphoma (FL). Following its approval, several trials investigating various PI3Kδ inhibitors as single agents or in combination with chemoimmunotherapy or other molecular targeted agents in CLL and indolent NHL (iNHL) have uncovered some severe autoimmune related toxicities. This review discusses and summarizes the biologic basis and the clinical experience of the PI3Kδ inhibitors in indolent B-cell malignancies.     

Histological and immunophenotypic changes in 59 cases of B-cell non-Hodgkin's lymphoma after rituximab therapy

Rituximab is a chimeric monoclonal antibody that recognizes the CD20 antigen. It has been used to treat B-cell non-Hodgkin lymphoma (B-NHL), but recently rituximab resistance has been a cause for concern. We examined histological and immunohistochemical changes in 59 patients with B-NHL after rituximab therapy. The patients comprised 32 men and 27 women with a median age of 59 years. Pre-rituximab specimens comprised 34 follicular lymphomas (FL), 11 diffuse large B-cell lymphomas (DLBCL), 10 mantle cell lymphomas, two marginal zone B-cell lymphomas (MZBCL), and two chronic lymphocytic leukemias (CLL). CD20 expression in lymphoma cells was evaluated by immunohistochemistry or flow cytometry. Post-rituximab materials were taken a median of 6 months (4 days to 59 months) after rituximab therapy. Sixteen cases (27%) showed loss of CD20 expression with four histological patterns: pattern 1, no remarkable histological change (FL, 5; DLBCL, 3; and CLL, 2); pattern 2, proliferation of plasmacytoid cells (FL, 2; DLBCL, 1; and MZBCL, 1); pattern 3, transformation to classical Hodgkin's lymphoma (FL, 1); and pattern 4, transformation to anaplastic large cell lymphoma-like undifferentiated lymphoma (FL, 1). Loss of CD20 was unrelated to the interval of biopsies, treatment regimen, clinical response, and frequency of rituximab administration. Loss of CD20 within 1 month of rituximab therapy (3/14, 21%) and regain of CD20 (2/7, 29%) were not frequent. CD20-positive relapse with transformation occurred most frequently in cases of early relapse. In conclusion, B-NHL showed various histological and immunophenotypic changes after rituximab therapy, including not only CD20 loss but also proliferation of plasmacytoid cells or transformation to special subtypes of lymphoma. ( Cancer Sci 2009; 100: 54–61)     

侵袭型非霍奇金淋巴瘤合并纯红细胞再生障碍性贫血

目的:研究侵袭性非霍奇金淋巴瘤并发纯红细胞再生障碍性贫血(PRCA)的临床特点和治疗结果。方法:报告两例分别并发于非特指型外周T细胞淋巴瘤(PTCL-NOS)和弥漫大B细胞淋巴瘤(DLBCL)的PRCA,并复习相关文献。结果:在联合化疗治疗后,DLBCL及其相关的PRCA均获完全缓解,而PTCL-NOS虽获缓解,但其相关的PRCA未好转,加用泼尼松治疗后PRCA缓解。结论:NHL相关的PRCA在联合化疗或免疫抑制治疗后可获完全缓解,且可不需维持治疗。     

Screening and early diagnosis in lung cancer

Over the last few years, several monoclonal antibodies have been investigated in patients with B-cell lymphoid malignancies. Rituximab is the most important monoclonal antibody of clinical value in these disorders. Rituximab is an IgG1 chimeric antibody containing murine light- and heavy-chain variable region sequences and human constant region sequences. Since approval in 1997, rituximab has become the standard of care in follicular B-cell lymphoma, chronic lymphocytic leukemia (CLL) and aggressive lymphoma when combined with chemotherapy. Higher clinical benefits of rituximab can be seen in patients with CLL when it is added to other chemotherapeutic agents. Several recent reports have suggested that in patients with CLL, rituximab combined with purine nucleoside analogs (PNAs) or PNAs and cyclophosphamide may improve the results with acceptable toxicity, both in previously untreated and refractory/relapsed patients. The randomized, multinational Phase III study (REACH trial) has shown that rituximab combined with fludarabine and cyclophosphamide (R-FC regimen) results in 10 months longer progression-free survival, and higher overall response and complete response rates than fludarabine and cyclophosphamide (FC regimen) in previously treated patients. The German CLL study group initiated a multicenter, multinational Phase III trial, CLL8, to evaluate the efficacy and tolerability of R-FC versus FC for the first-line treatment of patients with advanced CLL. The overall response rate was significantly higher in the R-FC arm (95%) compared with FC (88%). The complete response rate in the R-FC arm was 44% compared with 27% in the FC arm. The recently updated analysis has demonstrated longer overall survival in the R-FC group. Recent clinical observations have revealed that combinations of rituximab with pentostatin and cyclophosphamide, or cladribine and cyclophosphamide are also highly active regimens in previously untreated CLL. In addition, the results of treatment with high-dose methylprednisolone in combination with rituximab in advanced CLL resistant to fludarabine have been reported recently by several groups. However, available therapies are only partially effective in CLL, exposing an obvious need to develop new, more specific and active drugs. Recently, several new anti-CD20 monoclonal antibodies have been developed and are now being evaluated in clinical trials.     

Rituximab in Hodgkin lymphoma: is the target always a hit?

In 1997, the anti-CD20 monoclonal antibody (MAb) rituximab became the first MAb approved for clinical use in oncology, and ushered in a new era of rationally designed targeted agents in cancer therapeutics. It is currently approved for use in non-Hodgkin lymphoma (NHL), chronic lymphoid leukemia (CLL), and rheumatoid arthritis (RA). Rituximab is non-mutagenic, associated with low treatment-related toxicity, and few, if any, long term adverse events, making it an attractive agent to be tried in off-label settings like Hodgkin lymphoma (HL). HL consists of two distinct subtypes - classic HL (cHL) and lymphocyte predominant HL (LPHL). CD20 is present in virtually all patients with LPHL, and in a significant minority of patients with cHL. In this CD20 positive sub-population, the use of rituximab is a rational intervention strategy. Rituximab has been used in patients with cHL as well as LPHL with good efficacy. In this article, we provide a clinically-oriented overview of the use of rituximab in the different sub-types of HL, and report updated results of our series of 8 LPHL patients treated with rituximab. A systematic review of the literature is also presented.     

慢性淋巴细胞白血病的Richter’s征转化

目的:探讨Richter’s征(RS)的临床特征、预测指标、治疗和预后因素。方法:报告2例慢性淋巴细胞白血病(CLL)向RS转化并结合文献进行复习。结果:患者表现为进行性淋巴结肿大,伴乏力、盗汗,经血细胞形态学、免疫分型确定存在CLL克隆,淋巴结病理1例示弥漫性大B细胞淋巴瘤、另1例为小B细胞淋巴瘤向大细胞淋巴瘤转化。结论:RS为少见疾病,预后较差,诊断时需有病理证实CLL向侵袭性淋巴瘤转化,治疗应采用含利妥昔单抗的多药联合化疗,年轻患者如对初始治疗反应较好且有合适供体应进行异基因移植。     

Antik?rpertherapie bei malignem Lymphom

The availability of monoclonal antibodies has revolutionized the therapy of malignant lymphoma. By adding rituximab to the therapeutic arsenal, response rates, progression-free survival and even overall survival could be improved for several lymphoma entities. Ritxuimab is used as part of induction and maintenance therapy as well as in the relapse situation for follicular lymphoma, mantle cell lymphoma, diffuse large B cell lymphoma and chronic lymphocytic leukemia (CLL). The successors, ofatumumab and obinutuzumab are currently being tested in clinical trials. Other antibodies target CD22, CD52 and CD80. The CD52 targeting antibody alemtuzumab is approved for fludarabine refractory CLL by the Food and Drug Administration (FDA) and the European Medicines Agency (EMA) and is also effective in patients with high risk cytogenetics. Apart from conventional antibodies, the bispecific T-cell engager (BiTE) single-chain variable fragments (scFv) antibody blinatumomab is currently being tested in clinical trials. This review gives an overview of antibody therapy for malignant lymphoma.     

Rituximab plus fludarabine and cyclophosphamide or other agents in chronic lymphocytic leukemia

Over the last few years, several monoclonal antibodies have been investigated in patients with B-cell lymphoid malignancies. Rituximab is the most important monoclonal antibody of clinical value in these disorders. Rituximab is an IgG1 chimeric antibody containing murine light- and heavy-chain variable region sequences and human constant region sequences. Since approval in 1997, rituximab has become the standard of care in follicular B-cell lymphoma, chronic lymphocytic leukemia (CLL) and aggressive lymphoma when combined with chemotherapy. Higher clinical benefits of rituximab can be seen in patients with CLL when it is added to other chemotherapeutic agents. Several recent reports have suggested that in patients with CLL, rituximab combined with purine nucleoside analogs (PNAs) or PNAs and cyclophosphamide may improve the results with acceptable toxicity, both in previously untreated and refractory/relapsed patients. The randomized, multinational Phase III study (REACH trial) has shown that rituximab combined with fludarabine and cyclophosphamide (R-FC regimen) results in 10 months longer progression-free survival, and higher overall response and complete response rates than fludarabine and cyclophosphamide (FC regimen) in previously treated patients. The German CLL study group initiated a multicenter, multinational Phase III trial, CLL8, to evaluate the efficacy and tolerability of R-FC versus FC for the first-line treatment of patients with advanced CLL. The overall response rate was significantly higher in the R-FC arm (95%) compared with FC (88%). The complete response rate in the R-FC arm was 44% compared with 27% in the FC arm. The recently updated analysis has demonstrated longer overall survival in the R-FC group. Recent clinical observations have revealed that combinations of rituximab with pentostatin and cyclophosphamide, or cladribine and cyclophosphamide are also highly active regimens in previously untreated CLL. In addition, the results of treatment with high-dose methylprednisolone in combination with rituximab in advanced CLL resistant to fludarabine have been reported recently by several groups. However, available therapies are only partially effective in CLL, exposing an obvious need to develop new, more specific and active drugs. Recently, several new anti-CD20 monoclonal antibodies have been developed and are now being evaluated in clinical trials.     

CD5+ true SLL/CLL with plasmacytic differentiation and an unusual 1p36 translocation: case report and review of the literature

Lymphoplasmacytic lymphoma (LPL) and small lymphocytic lymphoma/chronic lymphocytic leukemia (SLL/CLL)are distinct clinicopathologic entities. Although some cases of SLL/CLL may show plasmacytic differentiation and be associated with monoclonal immunoglobulin in serum, such cases appear to be very rare, and if plasma cell differentiation were marked, differentiation of SLL/CLL from LPL could be difficult. We report a rare case of true CD5-positive small lymphocytic lymphoma/chronic lymphocytic leukemia with unequivocal plasmacytic differentiation. This case also showed an abnormality of chromosome 1p36 not previously described in small lymphocytic lymphoma/chronic lymphocytic leukemia.     

Rituximab using a thrice weekly dosing schedule in B-cell chronic lymphocytic leukemia and small lymphocytic lymphoma demonstrates clinical activity and acceptable toxicity.

PURPOSE: Rituximab has been reported to have little activity in small lymphocytic lymphoma (SLL)/chronic lymphocytic leukemia (CLL) and to be associated with significant infusion-related toxicity. This study sought to decrease the initial toxicity and optimize the pharmacokinetics with an alternative treatment schedule. PATIENTS AND METHODS: Thirty three patients with SLL/CLL received dose 1 of rituximab (100 mg) over 4 hours. In cohort I (n = 3; 250 mg/m(2)) and cohort II (n = 7; 375 mg/m(2)) rituximab was administered on day 3 and thereafter three times weekly for 4 weeks using a standard administration schedule. Cohort III (n = 23; 375 mg/m(2)) administered rituximab similar to cohort II for the first two treatments and then over 1 hour thereafter. RESULTS: A total of 33 CLL/SLL patients were enrolled; only one patient discontinued therapy because of infusion-related toxicity. Thirteen patients developed transient hypoxemia, hypotension, or dyspnea that were associated with significant changes in baseline interleukin-6, interleukin-8, tumor necrosis factor alpha, and interferon gamma compared with those not experiencing such reactions. Infusion-related toxicity occurred more commonly in older (median age 73 v 62 years; P =.02) patients with no other pretreatment clinical or laboratory features predicting occurrence of these events. The overall response rate was 45% (3% CR, 42% PR; 95% CI 28% to 64%). Median response duration for these 15 patients was 10 months (95% CI, 6.8-13.2; range, 3 to 17+). CONCLUSION: Rituximab administered thrice weekly for 4 weeks demonstrates clinical efficacy and acceptable toxicity. Initial infusion-related events seem to be cytokine mediated and resolve by the third infusion making rapid administration possible. Future combination studies of rituximab with other therapies in CLL seem warranted.     

SOHO State of the Art Updates and Next Questions | Management of Most Difficult Cases of Chronic Lymphocytic Leukemia: Relapse After Both BTK and BCL2 Inhibition and Richter Transformation

The introduction of targeted therapies in chronic lymphocytic leukemia (CLL) has ushered in a new era in which patients achieve better control of their disease, survive longer, and experience fewer toxicities than before. Despite this progress, a subgroup of patients with CLL will develop resistance to both Bruton tyrosine kinase (BTK) and B-cell lymphoma 2 inhibitors. In addition, a subgroup of CLL cases will transform into aggressive lymphoma – called Richter transformation – either before or during targeted therapy. These two subgroups of patients have a poor prognosis, and available therapies lead to long-term remission in only a minority of patients. In this paper, two cases are presented that are reflective of these difficult scenarios. In the first case, a patient with CLL, complex karyotype, del 17p, and a mutation in TP53 experiences progression after ibrutinib, venetoclax, bendamustine, rituximab, and idelalisib. In the second case, a patient with CLL and del 17p develops a Richter transformation to diffuse large B-cell lymphoma after treatment with obinutuzumab, chlorambucil, ibrutinib, venetoclax, and idelalisib. The aggressive lymphoma is refractory to chemoimmunotherapy, and she expires. The literature pertaining to these two scenarios is reviewed, including the role of available targeted therapies, chemoimmunotherapy, and hematopoietic cell transplantation. Emerging novel therapies, including reversible BTK inhibitors and CAR T cell therapy, are discussed.     

慢性淋巴细胞白血病的Richter＇s征转化

目的：探讨Richterg征（RS）的临床特征、预测指标、治疗和预后因素。方法：报告2例慢性淋巴细胞白血病（CLL）向RS转化并结合文献进行复习。结果：患者表现为进行性淋巴结肿大,伴乏力、盗汗,经血细胞形态学、免疫分型确定存在CLL克隆,淋巴结病理1例示弥漫性大B细胞淋巴瘤、另1例为小B细胞淋巴瘤向大细胞淋巴瘤转化。结论：RS为少见疾病,预后较差,诊断时需有病理证实CLL向侵袭性淋巴瘤转化,治疗应采用含利妥昔单抗的多药联合化疗,年轻患者如对初始治疗反应较好且有合适供体应进行异基因移植。     

Community-based phase II trial of pentostatin, cyclophosphamide, and rituximab (PCR) biochemotherapy in chronic lymphocytic leukemia and small lymphocytic lymphoma

We conducted a multicenter, community-based phase II trial of PCR biochemotherapy (pentostatin 4 mg/m2, cyclophosphamide 600 mg/m2, and rituximab 375 mg/m2) every 3 weeks for up to 6 cycles in patients with chronic lymphocytic leukemia (CLL) or small lymphocytic lymphoma (SLL). The study was stopped after enrolling 24 patients because of diminished investigator interest after 8 patients discontinued treatment because of adverse events, and 5 others died during treatment. The median age of patients was 69 years; 11 patients were over age 70, and 71% had Rai stage III or IV disease. The response rate among the 17 evaluable patients who completed 3 cycles of therapy was 58% (35%-81%, 95% confidence interval), with 2 complete responders (both greater than 70 years of age) and 7 partial responders. No patients developed progressive disease while receiving PCR. This is the first report of a trial in CLL utilizing a combination of purine analog, alkylator, and rituximab, in which most patients were older than 65 years and had high-risk disease. PCR is active in CLL/SLL, but appears to be less active and associated with more complications in the community setting, compared to trials with younger, lower risk patients who travel to academic referral centers for treatment.     

Relationship between venetoclax exposure,rituximab coadministration,and progression‐free survival in patients with relapsed or refractory chronic lymphocytic leukemia: demonstration of synergy

Venetoclax is indicated at a dosage of 400 mg daily (QD) for the treatment of patients with chronic lymphocytic leukemia (CLL) with 17p deletion who have received at least 1 prior therapy. Ongoing trials are evaluating venetoclax in combination with CD20 targeting monoclonal antibodies, such as rituximab. The objective of this research was to characterize the relationship between venetoclax exposures and progression‐free survival (PFS) and to evaluate the effect of rituximab coadministration on PFS in patients with relapsed or refractory (R/R) CLL/small lymphocytic lymphoma (SLL). A total of 323 patients from 3 clinical studies of venetoclax, with and without rituximab coadministration, were pooled for the analyses. A time‐variant relative risk survival model was used to relate plasma venetoclax concentrations and rituximab administration to PFS. Demographics and baseline disease characteristics were evaluated for their effect on PFS. A concentration‐dependent effect of venetoclax on PFS and a prolonged synergistic effect of 6 cycles of concomitant rituximab were identified. The 17p deletion chromosomal aberration was not identified to affect the PFS of patients treated with venetoclax. A venetoclax dose of 400 mg daily QD was estimated to result in a substantial median PFS of 1.8 years (95% confidence interval [CI], 1.7‐2.1), whereas the addition of 6 cycles of rituximab was estimated to increase the median PFS to 3.9 years (95% CI, 2.8‐5.6). The analysis demonstrates a concentration‐dependent effect of venetoclax on PFS and also a synergistic effect with rituximab. Combining venetoclax with the CD20 targeting monoclonal antibody rituximab in R/R CLL/SLL patients provides substantial synergistic benefit compared with increasing the venetoclax monotherapy dose.