Abstract
BACKGROUND: While generally ineffective in relapsed diffuse large B cell lymphoma (DLBCL), immune checkpoint inhibitors (ICIs) may hold greater promise in untreated, immunocompetent patients. We previously reported safety and early efficacy of pembrolizumab plus rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (PR-CHOP) in a phase I trial of untreated DLBCL, noting responses in 90% of patients (complete response 77%) and a 2-year progression-free survival (PFS) of 83%. We herein report long-term safety and efficacy at 5-year follow up. PATIENTS AND METHODS: Adult patients with untreated DLBCL or grade 3b follicular lymphoma, intended to receive 6 cycles of R-CHOP were eligible. Patients (N = 30) were treated with pembrolizumab 200 mg IV and R-CHOP in 21-day cycles for 6 cycles. RESULTS: At median follow up of 4.8 years, 5-year PFS was 71% (CI, 54%-94%) and 5-year overall survival was 83% (CI, 71%-98%). Immune-related adverse events (IRAEs) occurred in 7 (23%) patients (10% grade 3/4). Three IRAEs (rash, thyroiditis, rheumatoid arthritis) occurred beyond 3 months of treatment completion. PD-L1 tumor expression was documented in 19 of 23 (83%) tested patients. None of the 19 patients who had any PD-L1 expression have relapsed, whereas 2 out of the 4 patients with no PD-L1 expression have relapsed. CONCLUSION: PR-CHOP has led to durable responses in most patients, with the best outcomes in PD-L1-expressing disease. Furthermore, the safety profile was manageable, with no consistent pattern of late events. These data support ongoing strategies incorporating ICIs in frontline DLBCL therapy and confirmation of predictive biomarkers including tumor PD-L1 expression.