Safety and Toxicity Profile of Pembrolizumab (PEM) in Combination with ICE Chemotherapy Followed By Autologous Stem Cell Transplantation for Relapsed/Refractory Classical Hodgkin Lymphoma: No Impairment in Stem Cell Mobilization or Engraftment

Background: Despite excellent outcomes in the front-line management of classical Hodgkin lymphoma (cHL), patients with relapsed or refractory disease typically undergo second-line cytotoxic chemotherapy before proceeding to consolidation with autologous hematopoietic stem cell transplant (autoHSCT). Pre-transplant F18-FDG-PET imaging is a well-established predictor of outcomes following autoHSCT; a complete metabolic response (CMR) to second-line therapy defined as a Deauville score 1-3 predicts a favorable outcome and is a requirement for transplant at many centers. The PD-1 pathway plays an important role in the pathogenesis of cHL and checkpoint inhibition with agents including PEM and nivolumab have shown efficacy as monotherapy in heavily pretreated disease. We hypothesized that the addition of PEM to ICE (ifosfamide, carboplatin, and etoposide) chemotherapy will increase the rate of CMR by PET-CT prior to autoHSCT without impairing the mobilization of peripheral blood progenitor cells (PBPC) or engraftment. Here we present interim safety and toxicity data from this ongoing trial (NCT03077828) including the yields of PBPC mobilization and engraftment.

Methods: Enrollment criteria include patients age >18 years medically fit for autoHSCT with relapsed/refractory cHL and excludes those with prior PD-1 inhibitor exposure, CNS involvement, more than 2 prior regimens or history of autoimmune disease. Patients are treated with 2 cycles of PEM 200 mg IV on day 1 in combination with ICE chemotherapy (ifosfamide 5000 mg/m2 day 2 CIV over 24hr, carboplatin AUC 5 IV day 2, etoposide 100 mg/m2 IV days 1-3) on a Q21 day cycle. PBPC mobilization and harvest are performed per institutional protocol on recovery post-cycle #2. A cycle of PEM 200 mg IV is then administered as monotherapy followed by response assessment with PET-CT. Patients with Deauville scores ≤3 proceed to autoHSCT per institutional protocol. A third cycle of PEM+ICE is optional following the PET-CT assessment. Neither the conditioning regimen nor management during transplantation is dictated by the protocol.

Results: As of July 2019, 23 of 40 planned patients have evaluable safety and toxicity data. One patient had inconclusive pathology and was removed from study after one cycle of PEM-ICE but is included for this report. The median age was 32 (range 19-62) and 17 of 23 patients were females (74%). 8 patients were refractory to first-line therapy, and 9 relapsed within one year of treatment. 19 patients had received ABVD. Following protocol directed therapy, all but one patient had successful mobilization and collection; one had a severe allergic reaction to filgrastim and underwent bone marrow harvest instead. 16 patients collected in a single day of apheresis; the remainder collected within 4 days. The median number of stem cells harvested was 12.6 x 10⁶ CD34+ cells/kg (range 4.2 - 46.1 x 10⁶/kg). 3 patients underwent the 3^rd cycle of PEM + ICE chemotherapy. 3 patients had Deauville scores >3 on FDG-PET response assessment; two had biopsies showing only benign processes and proceeded to transplant. Following stem cell reinfusion, all patients successfully engrafted, with a median time to absolute neutrophil and platelet recovery of 11 days (range: 9 - 24) and 12 days (range: 9 - 23), respectively.

The combination of PEM + ICE chemotherapy was well tolerated. There were no reports of pneumonitis, colitis, hepatitis, or endocrinopathies. The most common toxicities were cytopenias, mucositis, diarrhea and febrile neutropenia. A single death on protocol was deemed secondary to advanced cardiovascular disease discovered mid-treatment during the patient's pre-transplant assessment. There was no clinical evidence to suggest an inflammatory process resulting in the cardiac arrest.

Conclusions: The combination of PEM with ICE chemotherapy in relapsed / refractory cHL appears tolerable and safe. We found no significant hindrance to peripheral blood stem cell harvest and PEM- related AEs were uncommon. Additionally, pre-treatment with a checkpoint inhibitor prior to autoHSCT appears safe thus far and does not appear to delay engraftment.