Outcomes and prognostic factors of patients diagnosed with relapsed/refractory primary B-cell lymphoma: A retrospective study.

7081 Background: PMBCL is an aggressive form of large B-cell lymphoma (LBCL) but has a unique gene expression profiling signature that more closely resembles Hodgkin’s lymphoma. Treatment of R/R PMBCL is largely extrapolated from trials in LBCL with few PMBCL patients included. Randomized trials leading to use of CART as second line treatment for patients with primary refractory or early relapsed LBCL enrolled ≤ 10% PMBCL patients (ZUMA-7 and TRANSFORM). In the rituximab era, there is a paucity of data on the efficacy and outcomes of salvage therapy followed by high-dose chemotherapy and autologous stem cell transplant (HDT/ASCT) in PMBCL. Methods: We conducted a retrospective study of patients with PMBCL, histologically confirmed at the University of Michigan, diagnosed between 2001 and 2023. Results: 70 patients were included with a median age of diagnosis of 31.5 years and 57% female. R-DA-EPOCH was the most commonly used first line therapy (FLT) in 58 patients (83%). 10 patients (14%) were treated with R-CHOP with or without consolidative radiation. 65 patients had end of treatment (EOT) PET/CT: 45 (69%) patients achieved a Deauville (D) 1-3 response, 15 (23%) had D4 response, 5 (8%) had D5 response. 4 (26%) of patients with D4 response and all patients with D5 response ultimately developed R/R disease. 5 had EOT response assessed by CT and all deemed to have complete response. 16 patients (23%) developed R/R disease with a median time to relapse of 8.3 months. All relapses occurred within 2 years: 5 patients with primary refractory disease, 10 patients with relapse 12 months. Platinum based chemotherapy with RICE, RDHAP or RGemOx were the most common salvage regimens (N=11) with ORR 60% among evaluable patients. 5 patients received HDT/ASCT with ORR of 80% and CR rate of 80%. Only 1 patient progressed following ASCT, who had relapsed >12 months after FLT. 9 patients (13%) had high-risk extranodal disease (EN) such as renal, adrenal or breast sites with 2 patients (11%) developing CNS relapse. At a median follow up time of 6.5 years, 5-year PFS and OS for the entire cohort was 76% and 96%, respectively. For patients with R/R disease, 5-year PFS and OS was 49% and 84%, respectively. Conclusions: We report high response rates to platinum-based salvage chemotherapy in the rituximab era, even with primary refractory or early relapsed disease. Higher PFS and OS suggests improved outcomes with HDT/ASCT compared to historical outcomes in R/R LBCL (SCHOLAR-1). Larger prospective studies are needed to determine whether HDT/ASCT or CART is the optimal approach in R/R PMBCL. Table: see text