Consolidative breast radiotherapy and prophylactic high-dose methotrexate are important first-line treatments for primary breast diffuse large B-cell lymphoma patients treated with R-CHOP-like regimens

Purpose: Primary breast diffuse large B-cell lymphoma (PB-DLBCL) is a rare form of extranodal DLBCL. In this study, we aimed to determine the patterns of relapse and the optimal treatment strategy for PB-DLBCL in the rituximab era. Methods We retrospectively collected data from Chinese Southwest Oncology Group-affiliated institutes. Patients diagnosed with PB-DLBCL from 2008 to 2019 and treated with rituximab plus cyclophosphamide, doxorubicin, vincristine, prednisone (R-CHOP) or R-CHOP-like regimens were included. Results A total of 135 PB-DLBCL patients treated with R-CHOP or R-CHOP-like regimens were eligible for this study. With a median follow-up of 43 months, the 5-year overall survival (OS) and progression-free survival (PFS) rates were 84.7% and 69.6%, respectively. Continuous treatment failure was observed, especially affecting the breast and central nervous system (CNS). Consolidative RT significantly reduced the risk of breast relapse (p = 0.013). Relapse in CNS were detected in 13 (9.6%) patients, of whom 4 had received intrathecal prophylaxis and 9 had not received CNS prophylaxis. None of the patients who received high-dose methotrexate (HD-MTX) had CNS relapse. CNS relapse risk was reduced by HD-MTX (p = 0.036). Furthermore, we screened the genetic mutation profile of PB-DLBCL and found that MYD88 and/or CD79B mutations were present in all patients with CNS relapse, whereas patients with MYD88 and/or CD79B mutations who received HD-MTX did not experience CNS relapse. Conclusions Our results indicate that consolidative RT decreased the risk of breast relapse. Prophylactic HD-MTX reduced the risk of CNS relapse, especially in patients with MYD88/CD79B mutations.