We performed a multicenter, retrospective study to better understand the underlying biology, survival outcomes, and optimal treatment of PBL in a contemporary cohort of patients in the US. To our knowledge, this is the largest real-world cohort of PBL patients to date.
The main finding of this study was the markedly improved median OS in our cohort (5.0y) compared with a recently published international cohort (1.4y), albeit with similar median PFS (1.4y vs 8.4 mo).12 This discrepancy may be explained by differences in second-line therapies available during the time frame of the two studies. Di Ciaccio et al. enrolled from 1999 to 2020, with only 35% of patients diagnosed after 2015, whereas we enrolled from 2005 to 2022, with 70% diagnosed after 2014. It is possible that increased use of modern biological agents in our more contemporaneous cohort explains the improvement in OS.
The results of our study are broadly consistent with the current understanding of PBL. Known lymphoma risk factors that are usually captured in the IPI, such as advanced age, stage III/IV, ECOG ≥ 2, and LDH elevation, were associated with poor OS in our cohort.18 Consistent with Di Ciaccio et al., we also found EBV negativity to be associated with poor PFS.12
While there is mixed evidence regarding the prognostic impact of MYC rearrangement in PBL,12,13,19,20 our results suggest that MYC+/EBV- PBL may represent an aggressive disease subtype; however, this requires further exploration, especially as data on MYC rearrangement was missing in many patients. EBV-positivity has been associated with different genetic features in Burkitt lymphoma (BL) when compared to EBV-negative cases. Recently, investigators identified that EBV + BL is characterized by fewer driver mutations, higher aberrant somatic hypermutation rates, and significantly more breakpoints upstream of MYC.21 Therefore, interaction of EBV and MYC in PBL may result in different pathobiology underlying the observed differential outcomes. Furthermore, the association between female sex and poor OS on UVA (albeit with no association on MVA) is intriguing and warrants further investigation, particularly since males tend to have worse survival outcomes in most other lymphoma subtypes.22,23 However, this observation may be related to the fact that male sex was predominant in the HIV-PBL cohort, which, in general, had better outcomes.
Despite improvement in median OS, PBL remains a difficult-to-treat disease, as demonstrated by a 5-year OS rate of 50% in our cohort. Survival outcomes differed by immune status: HIV-PBL had the best outcomes (median OS 7.2y, median PFS 1.8y), while PTLD-PBL had the worst outcomes (median OS 1.1y, median PFS 1.0y). This may be due to a partially reversible immunodeficiency in PLWH, especially as about a third of the HIV-PBL cohort was previously ART-naïve. The poor survival outcomes of PTLD-PBL suggest this may represent an aggressive subtype, possibly related to the mostly irreversible, underlying, severe iatrogenic immunodeficiency in post-transplant patients. The underlying histopathologic features of this entity represent an area of future investigation. While there were various underlying immunosuppressed states in the OIS-PBL cohort, many were LPDs, raising the possibility that the PBL diagnosis represented a transformation event. Further investigation into the biology and clinical outcomes of this subgroup is warranted.
The optimal treatment of PBL remains poorly defined due to the rarity of the disease and paucity of prospective clinical trials. While early studies of HIV-associated non-Hodgkin lymphomas suggested superior outcomes with EPOCH compared with CHOP and prompted NCCN guidelines to favor higher-intensity regimens, more recent retrospective studies have increasingly suggested no benefit to such an approach in PBL.11,12,24,25 Our results similarly found no benefit with the use of EPOCH or other high-intensity regimens in the 1L setting over CHOP and therefore do not support the use of higher-intensity regimens, which are subject to higher rates of treatment-related morbidity and mortality. However, none of these are randomized prospective studies.
Similarly, despite promising results in small, retrospective case series,7 proteasome inhibitors failed to show frontline benefit in a recent multicenter study,12 consistent with the findings in our cohort. Nevertheless, our study was not powered to definitively address the merit of biological agents classically used for plasma cell malignancies, such as bortezomib, daratumumab, and lenalidomide, in the management of PBL. However, the improved OS despite a similar PFS after 1L therapy in our US cohort could indicate a role for these agents in PBL. Prospective and ideally randomized clinical trials will be necessary to address this question. At present, a prospective randomized clinical trial in the US explores the combination of daratumumab with EPOCH,26 while another study sponsored by the Fondazione Italiana Linfomi studies the combination of daratumumab, bortezomib, and dexamethasone for relapsed/refractory (r/r) PBL.27
While there is no superior chemotherapeutic regimen in the 1L setting, RT and ASCT consolidation in our study were associated with improvements in OS, albeit with the inherent bias that to receive these treatments most patients would have needed first to achieve a complete response to initial therapy. However, as only 8% of the entire cohort underwent consolidative ASCT in first remission, the benefit of ASCT should be interpreted with caution and considered on a case-by-case basis in select, high-risk patients.
In contrast, the use of CNS prophylaxis was not associated with OS and had no apparent effect on the risk of CNS recurrence, although the numbers were too small for firm conclusions. This is in line with recent observations in DLBCL that indicate a lack of benefit of CNS prophylaxis irrespective of modality.28,29 Thus, the decision to use CNS prophylaxis in PBL should be highly individualized.
Several small studies have investigated the management of r/r PBL with chemotherapeutic regimens such as ICE, with or without agents like daratumumab and lenalidomide.30,31,32,33 We gathered data on 105 patients who underwent treatment in the r/r setting, and a comparison of survival outcomes using various 2L regimens, as well as the impact of use of biologic agents in the 2L setting will be addressed in future analyses. Further, while CAR T-cell therapy has revolutionized the treatment landscape of both DLBCL and multiple myeloma, its use in PBL has been limited. To our knowledge, there are only three published cases using CAR T-cell therapy in r/r PBL. One achieved a complete metabolic response, followed by disease progression at 5 months post-CD19-directed CAR T-cell infusion.34 Two additional patients achieved complete remissions in response to BCMA-directed CAR T-cell products, with CR documented at 6 and 14 months post-infusion, respectively.35,36 Herein, we report four patients treated with CAR T-cell therapy (CD19-directed, n = 3; unknown target, n = 1) with disappointing outcomes. It is unclear if the expression of CD19 and/or BCMA played a role in treatment choice. More data is needed regarding the safety, efficacy, and optimal target antigen of CAR T-cell therapies in the management of r/r PBL.
There are several limitations to this study. Namely, given the retrospective nature of data collection, there was considerable variation in data availability between participating institutions. While some clinicopathologic variables were missing, we addressed missing data bias by using multiple imputation for multivariable analyses. Further, no centralized pathologic review was done to confirm a diagnosis of PBL in each patient; however, all participating institutions were major academic centers with experienced hematopathology departments.
Despite the limitations of our study, it has several strengths, including our large sample size and granular, patient-level data. This allowed us to control for possible confounders by using propensity score adjustment and therefore significantly reduce bias. Further, this study expands the existing literature on this rare entity, augments findings of a recently published cohort from Australia, the UK, Canada, and Singapore, and at the same time contrasts them with our contemporary US cohort.12
The prognosis of PBL has significantly improved over recent decades, particularly for HIV-PBL. While no optimal treatment has been established, more intense cytotoxic regimens may not confer a significant survival benefit. Although biological agents commonly used for plasma cell dyscrasias have been suggested to be of benefit based on small case series, their frontline use was not associated with improved outcomes in our study, and their role in PBL remains to be defined. This can only be done definitively in well-designed, prospective, and randomized clinical trials. Better understanding of the pathogenesis that underlies PBL based on oncogenic events and interactions with the host immune environment may also lead to more rationally targeted therapies and further improved outcomes.