Phase I Study Combining Ibrutinib with Rituximab, Ifosfamide, Carboplatin, and Etoposide (R-ICE) in Patients with Relapsed or Primary Refractory Diffuse Large B-Cell Lymphoma (DLBCL): NCI-Cancer Therapeutics Evaluation Program (CTEP) #9588

Background: In the post-rituximab era, half the patients with relapsed or refractory (rel/ref) diffuse large B-cell lymphoma (DLBCL) fail to achieve a chemosensitive response with standard salvage therapy, and are thus ineligible to proceed to consolidative autologous stem cell transplantation (ASCT) with curative intent. The Bruton's tyrosine kinase inhibitor ibrutinib demonstrates single-agent activity in rel/ref DLBCL, predominately of the non-germinal center B-cell (non-GCB) phenotype, with minimal toxicity. This single center, NCI-CTEP sponsored phase I study is the first to evaluate the combination of ibrutinib with standard salvage therapy of rituximab, ifosfamide, carboplatin and etoposide (R-ICE) in transplant-eligible rel/ref DLBCL patients.

Methods: Patients with rel/ref DLBCL, including transformed B-cell non-Hodgkin lymphoma, are eligible for study. The phase I study design is a standard 3 x 3 dose escalation of ibrutinib at 420 mg (dose level [DL] #1), 560 mg (DL #2) and 840 mg (DL #3) on days 1-21 with standard dosing of R-ICE for 3 cycles, every 21 days. The primary objective is to determine safety and the maximum tolerated dose (MTD) of ibrutinib in combination with R-ICE. Secondary objectives include response rate according to computed tomography (CT) and functional imaging (FDG-PET) per Deauville criteria.

Results: To date, 16 patients are evaluable for toxicity, and 15 are evaluable for response. The median age of the 16 evaluable patients is 51 years (range 19-75 years). Histologies of the patients evaluable for response are: GCB DLBCL n=3, non-GCB DLBCL n=4, primary mediastinal large B-cell lymphoma n=4, and transformed chronic lymphocytic leukemia/small lymphocytic lymphoma (tCLL/SLL) n=4. There were no dose-limiting toxicities (DLTs) seen at DL #1 (n=3), 2 (n=3), or 3 (n=10, currently in expansion). Of the 16 patients evaluable for toxicity, 15 experienced expected and transient grade 3 or 4 hematologic toxicities with hematopoietic recovery prior to each cycle. The median number of cumulative platelet transfusions per patient for 3 cycles was 2 (range 0-11). Eleven of the 15 patients evaluable for response underwent chemotherapy-primed CD34+ hematopoietic progenitor cells (HPCs) apheresis procedures on study; 10 of the 11 patients successfully collected HPCs with a median of 5.6 x 10⁶CD34+/kg (range 1.7-8.6). The only patient that failed to collect HPCs was an HIV-positive patient at DL #3 in the setting of febrile illness. One patient experienced grade 3 atrial fibrillation/flutter and was subsequently removed from study per treating physician's decision. Per CT criteria, five patients achieved complete remission (CR), eight patients achieved partial remission (PR), and two patients had stable disease for an overall response rate of 87%. All eight patients with non-GCB DLBCL and tCLL/SLL that were evaluable for response achieved chemosensitive remission per CT criteria (CR=4, PR=4). Seven of the 15 total patients (47%) evaluable for response achieved a complete metabolic remission (Deauville 1-3) per FDG-PET, including all 4 patients of non-GCB phenotype.

Conclusions: Currently, no DLTs have been observed with ibrutinib at dosing up to 840 mg daily in combination with R-ICE. We are currently expanding DL #3. Manageable and expected hematologic toxicities have been observed. Importantly, hematologic toxicity has not resulted in failure to complete protocol therapy on-schedule or mobilize HPCs. Encouragingly, 87% of patients achieved a CT response (CR/PR) and 47% of patients achieved a complete metabolic remission per FDG-PET, including 100% of patients with non-GCB phenotype. These results compare favorably to historic cohorts. Given the safety and efficacy observed in this phase I, later phase studies for this treatment program are warranted.