Utilization of Autologous Stem Cell Transplant in Plasmablastic Lymphoma and Its Outcomes: A Population-Based Analysis

Introduction: Plasmablastic lymphoma (PBL) is a rare subtype of B-cell lymphoma with aggressive features and poor prognosis. It is known to be associated with immunocompromised states including HIV, organ transplantation, and EBV infection. Although PBL most closely resembles DLBCL with regards to its genetic aberration profile it lacks typical B-cell markers such as CD19, CD20, and PAX-5, rendering B-cell therapies such as rituximab ineffective. There are currently no consensus guidelines on an ideal first line chemotherapy regimen for the treatment of PBL but typically a chemotherapy combination such as DA-EPOCH, Hyper-CVAD, CODOX-M/IVAC is utilized, with addition of plasma cell-directed therapies including daratumumab emerging recently into the treatment landscape. Autologous stem cell transplantation in first complete remission (CR1) has been studied in few retrospective reviews and case series with promising data for prolonging survival but is not widely used. We aimed to perform an analysis of the NCDB to identify predictors of transplant in this population and patient outcomes. Methods: We conducted a retrospective cohort analysis of de-identified data accessed from the NCDB. A total of 3437 patient records were obtained of patients diagnosed with plasmablastic lymphoma between 2004-2017. Patients were excluded if histologic diagnosis was not confirmed, survival data was not available, if transplant status was unknown or contraindicated, or if the patient received allogeneic stem cell transplant. A total of 1296 patients were included in the final analysis. Patients were divided into two treatment groups based on receiving autologous stem cell transplant in CR1: ASCT and non-ASCT. Multivariable regression models were used to analyze predictors of receiving transplant and survival. Survival estimates were calculated using the Kaplan-Meier and Cox proportional hazard regression model. Results: Twenty patients (1.5%) received stem cell transplant in CR1. The median age for the whole cohort was 53 (43-67), the majority were non-Hispanic whites (64%), and treated at an academic/research program (40.8%). Of note, more patients in the ASCT group were treated at an academic center (73.7%) vs non-ASCT group (49.2%). No statistically significant predictors for selecting transplant in CR1 were found. Median overall survival in the ASCT group was 125.8 months (95% CI 56.8-194.9) compared to 43.5 months (95% CI 32.9-54.1) in the non-ASCT group (p=0.04). Increasing age (HR 1.01, 95% CI 1.01-1.02, p=0.002), and stage IV disease (HR 2.5, 95% CI 1.98-3.15, p<0.01) were associated with worse survival. Patients with private insurance (HR 0.67 95% CI 0.48-0.96, p=0.03) and Hispanic patients (HR 0.65, 95% CI 0.48-0.87, p=0.004) had better overall survival. Conclusion: To our knowledge, this is the largest population-based study of outcomes following autologous stem cell transplant in CR1 for treatment of PBL. Our findings are consistent with those of smaller case series, demonstrating an improved overall survival with the use of ASCT. It is also evident that transplant is being underutilized in this disease. Our data suggests that certain characteristics may predict survival. The low number of patients in the ASCT group precluded examination of predictors for selection of transplant.