Primary Effusion Lymphoma (PEL) and Primary Effusion-like Lymphoma (PEL-LL): A Comparative Study of Clinicopathologic Features and Outcomes

Abstract

Background: While PEL is a well-established distinct WHO entity, PEL-LL is poorly defined and has been characterized differently by different researchers. Over the years, it encompassed PEL that expressed mature B-cell markers, extra-cavitary solid PEL, and recently the HHV8-unrelated PEL-like lymphomas. For this study, we defined PEL-LL as PEL-like lymphomas expressing mature B-cell phenotype. We conducted this study to compare the clinicopathological characteristics of PEL and PEL-LL and their impact on clinical outcomes. Methods: To study the clinicopathologic characteristics, therapeutic interventions, overall survival (OS), disease-free survival (DFS), and prognostic factors, we compiled a pooled database of 381 cases of PEL and PEL-LL. Chi-square and t-test were used to test the statistical significance of differences in parameters. Kaplan-Meier survival curves were constructed. Cox proportional hazards model and Log-rank tests were used to assess the influence of clinicopathologic factors on OS and DFS. Results: A total of 381 (268 PEL, 113 PEL-LL) patients were identified. PEL and PEL-LL median ages were 51 and 74 (p < 0.0001), respectively. There was a male preponderance with M:F of 7 with PEL versus 2 with PEL-LL (p < 0.0001). The median OS was 6 months for PEL and 16 months for PEL-LL (p = 0.006). Compared to the thoracic cavity, involvement of the peritoneal cavity was associated with worse OS in both PEL and PEL-LL. Still, PEL-LL maintained better outcomes for each risk group (24 and 7 vs. 11 and 4 months, p < 0.0001). In the absence of HIV infection, PEL-LL has a superior OS to PEL (19 vs. 6 months, p = 0.002). However, HIV infection erases this survival advantage (6 vs. 6.5 months). In both entities, active treatment was associated with better OS (19 vs. 10 and 9 vs. 2 months, p < 0.0001). However, the untreated PEL-LL arm did as well as the treated PEL arm. Achieving CR as the best response to therapy in both PEL-LL and PEL was associated with superior OS (108 vs. 7 and 70 vs. 2 months, p < 0.0001). While dose-intense chemotherapy regimens did not impact OS in PEL-LL, they were associated with better OS in PEL (22 vs. 18 and 15 vs. 8 months, p = 0.03). Conclusions: This is the first study to compare PEL and PEL-LL expressing mature B-cell phenotype. It identifies key factors that impact OS that vary between the two entities. It also supports that PEL and PEL-LL represent two different disease entities regardless of their similar presentation.