Trends in Incidence and Survival of Patients With Primary Effusion Lymphoma in the United States: A Population Based Cohort Study.

Primary effusion lymphoma (PEL) is a rare and aggressive B-cell non-Hodgkin lymphoma (NHL) that predominantly affects patients with human immunodeficiency virus infection and is strongly associated with human herpes virus 8 (HHV-8) infection. Due to its rarity, the current understanding of PEL's epidemiology and management is largely derived from case reports and small retrospective studies. Using the SEER-17 database, we conducted a retrospective analysis of adults with pathologically confirmed primary effusion lymphoma diagnosed between 2001-2021. Patients were stratified into two time periods (2001-2010 and 2011-2021) to assess temporal trends. Age-adjusted incidence rates, relative survival (RS), overall survival (OS), and lymphoma-specific survival (LSS) were calculated using flexible parametric survival models. Competing risk analysis was performed to evaluate cumulative incidence of lymphoma-specific death. Among 236 patients (median age 51 years, 88% male), 82 were diagnosed in 2001-2010 and 154 in 2011-2021. Age-adjusted incidence rates increased from 1.0 to 1.6 cases per 10,000,000 person-years between periods (p = 0.004). Five-year RS improved from 21% to 37%, with median OS increasing from 4 to 12 months. On multivariable analysis, the more recent period showed significant improvements in OS (HR = 0.65; 95% CI, 0.44-0.97) and LSS (HR = 0.56; 95% CI, 0.36-0.86), with reduced cumulative incidence of lymphoma-specific death (HR = 0.49; 95% CI, 0.33-0.74). In our population-level analysis of PEL, we report a significant improvement in survival outcomes between 2001-2021, likely reflecting advances in both lymphoma treatment and HIV management. However, despite these improvements, OS remains low underscoring the need for prioritizing these patients to clinical trials with novel therapies.