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

## TL;DR

This study shows improved survival rates for a rare lymphoma linked to HIV over two decades, but outcomes remain poor.

## Contribution

First population-based analysis of primary effusion lymphoma trends in the U.S. using SEER data.

## Key findings

- Age-adjusted incidence of PEL increased from 1.0 to 1.6 cases per 10 million person-years between 2001–2010 and 2011–2021.
- Five-year relative survival improved from 21% to 37%, with median overall survival rising from 4 to 12 months.
- Recent period showed significant survival improvements, with reduced lymphoma-specific death risk (HR = 0.49).

## Abstract

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.