Primary breast diffuse large B‐cell lymphoma in the rituximab era: A retrospective study of the Chinese Southwest Oncology Group.

Background: Primary breast diffuse large B‐cell lymphoma (PB‐DLBCL) is a rare subtype of extranodal DLBCL, and the standard treatment remains controversial. In this study, we aimed to define the optimal treatment management in the rituximab era. Methods: A total of 5089 newly diagnosed DLBCL patients treated with rituximab‐containing immunochemotherapy between 2008 and 2019 from the Chinese Southwest Oncology Group‐affiliated institutes were identified, of whom 135 diagnosed with PB‐DLBCL were eligible for this analysis. Results: PB‐DLBCL accounted for 2.7% of all DLBCLs. With a median follow‐up of 4.2 years, the 5‐year overall survival and progression‐free survival rates were 84.8% and 71.6%, respectively. Breast and central nervous system (CNS) relapses were the main cause of treatment failure. We observed that consolidative breast radiotherapy (RT) significantly decreased breast relapse risk (5‐year risk, 2.9% vs. 20.1%, p = 0.007). The CNS relapse risk was lower for patients who received high‐dose methotrexate (HD‐MTX) than for patients who did not (5‐year risk, 0% vs. 15.2%, p = 0.015). We further screened the genetic mutation profile of 20 patients from two institutes, and found that MYD88 (25%) and CD79B mutations (25%) frequently occur in PB‐DLBCL. In addition, four patients with MYD88 and/or CD79B mutations experienced CNS relapse, while three patients with MYD88 and/or CD79B mutations who received HD‐MTX did not experience CNS relapse. Conclusion: Collectively, our results indicate combined modality therapy including rituximab‐containing immunochemotherapy and consolidative breast RT is a promising approach for PB‐DLBCL, while HD‐MTX is useful for preventing CNS relapse. [ABSTRACT FROM AUTHOR]