Impact of Cell-of-Origin and MYC/BCL2 Status on the Risk of Central Nervous System Relapse in Primary Breast Diffuse Large B-Cell Lymphoma.

[PURPOSE] Primary breast diffuse large B-cell lymphoma (DLBCL) is a rare entity with a distinct relapse pattern involving the central nervous system (CNS). However, data regarding predictors of CNS relapse in this population remain limited.

[MATERIALS AND METHODS] CNS relapse was retrospectively analyzed in two multicenter cohorts comprising 53 patients with newly diagnosed primary breast DLBCL, including a prospective trial and real-world cohort, all treated with rituximab-based immunochemotherapy. The impact of baseline clinical parameters, cell-of-origin, and MYC/BCL2 dual expression (DE) status on CNS relapse was assessed using a multivariate Cox regression model, separately conducted for the overall study set (n=53) and the immunohistochemical study set (n=36).

[RESULTS] By the CNS-International Prognostic Index (CNS-IPI), most patients were classified as low or intermediate risk; no patients were classified as high risk. With a median follow-up of 58.8 months, the 4-year risk of CNS relapse was 15.6% in the overall study set and 14.2% in the immunohistochemical set. MYC/BCL2 DE was identified in 14 patients (38.9%) and was significantly associated with increased risk of CNS relapse (4-year risk, 30.7% vs. 0%, p=0.001). Patients with non-germinal center B-cell-like subtype had a numerically higher risk of CNS relapse. However, in multivariate analysis, only MYC/BCL2 DE status was associated with CNS relapse. Synchronous bilateral involvement was also an independent predictor of CNS relapse in both study sets. CNS-IPI was not discriminatory for CNS relapse.

[CONCLUSION] MYC/BCL2 DE and synchronous bilateral breast involvement may help identify patients at higher risk for CNS relapse. Further studies are warranted.