Pembrolizumab (PEM) Added to ICE Chemotherapy Results in High Complete Metabolic Response Rates in Relapsed/Refractory Classic Hodgkin Lymphoma (cHL): A Multi-Institutional Phase II Trial

Introduction: Approximately 30-35% of patients with classic Hodgkin Lymphoma will prove refractory to frontline therapy or relapse subsequently. Traditional second-line chemotherapy regimens including ifosfamide, carboplatin, and etoposide (ICE) result in complete response rates of ~50%. Achievement of complete metabolic response (CMR) assessed by PET/CT imaging prior to autologous hematopoietic stem cell transplant (AHSCT) predicts favorable progression free survival (PFS) and overall survival (OS). PD-1 blockade is a well-established therapeutic strategy for the treatment of cHL. Pembrolizumab (PEM) is a checkpoint inhibitor targeting PD-1 currently FDA approved as monotherapy in relapsed cHL. We hypothesized that PEM in combination with ICE (PEM-ICE) chemotherapy would be a safe and effective regimen that would yield high CMR rates prior to AHSCT.

Methods: This single arm, phase II, multi-institutional clinical trial evaluated the addition of PEM to ICE chemotherapy in AHSCT eligible patients with relapsed and refractory cHL (NCT03077828). The regimen consisted of 21 day cycles of PEM 200 mg IV on day 1 with standard ICE including ifosfamide 5 g/m2 with MESNA as a 24hr continuous infusion on day 2, carboplatin AUC 5 IV (max 800 mg) on day 2, and etoposide 100 mg/m2/day IV on days 1 to 3. Two cycles of PEM-ICE were followed by stem cell mobilization/collection. One cycle of PEM 200 mg IV monotherapy was then administered. Our primary endpoint was the rate of CMR on PET/CT (PET2) imaging defined as a Deauville score of ≤ 3. Images were reviewed centrally. An optional third cycle of PEM-ICE was permitted for patients achieving CMR to allow for appropriate timing of AHSCT. Secondary objectives included clinical outcomes (PFS and OS), safety and tolerability, and transplantation related metrics including ability to collect stem cells and time to engraftment.

Results: A total of 42 patients were enrolled with 37 patients evaluable for the primary endpoint. Median age was 34 (19-70) with female predominance (n=27, 64%). 16 patients had primary refractory disease. The CMR rate assessed by PET/CT imaging following 2 cycles of PEM-ICE was 86.5% (95% CI, 71.2-95%), meeting our primary endpoint of improvement over historical outcomes to 70%. The PET2 ORR was 97.3% with 11% PR and 2.7% PD. PET2 scores were Deauville 1 in 45% (n=17), Deauville 2 in 27.0% (n=10), Deauville 3 in 8.1% (n=3), Deauville 4 in 13.5% (n=5), and Deauville 5 in 5.4% (n=2). New areas of PET-positivity in two cases were biopsied showing noncaseating granuloma in one case and EBV but no cHL in another. Five patients received the optional third cycle of PEM-ICE chemotherapy with 35 of the 37 evaluable patients proceeding to AHSCT. Seven patients had radiation as part of the conditioning regimen with an additional 4 patients receiving consolidative radiation following transplant. After a median follow up of 27 months, the median PFS was 26.9 months with survival probability at 24 months of 88.2% (Figure 1). Median OS was not reached with too few events but remained 95.1% at 27 months. The addition of PEM to ICE did not impair stem cell mobilization and all patients successfully collected, with 35 (87%) within 2 apheresis sessions (range 1-7). No patients had engraftment delays or failure. Of the 42 patients, all received at least one dose of PEM and were therefore eligible for toxicity analyses. 34 patients (81%) experienced adverse events (AEs) attributed to PEM and 22 patients (52.3%) had grade 3-4 AEs comprised of cytopenias, elevated AST/ALT, hyponatremia, hypophosphatemia, and fatigue. Five patients had severe AEs attributed to PEM which included anemia, back pain, decreased EF, fever, and thrombocytopenia. There were no significant PEM-related autoimmune events that delayed a patient's treatment on protocol. There were two grade 5 toxicities on the protocol including a patient with cardiac arrest during stem cell collection and a patient with acute respiratory distress syndrome attributed to engraftment syndrome. Both were judged "possibly" related to PEM.

Conclusions: Pembrolizumab with ICE chemotherapy is a tolerable and efficacious regimen with high CMR rate as assessed by PET/CT. Despite short follow up, patients had excellent PFS and OS in the post-transplant setting. The results support further investigation of PEM-ICE as second-line treatment for AHSCT eligible patients with relapsed and refractory classical Hodgkin lymphoma.

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