Primary breast diffuse large B-cell lymphoma characterized by CNS relapse and successful hematopoietic stem cell transplantation salvage therapy

Background: Primary breast diffuse large B-cell lymphoma (PB-DLBCL) is rare, with a high incidence of central nervous system (CNS) relapse. This study aims to investigate clinical characteristics, prognostic factors, and outcomes in Taiwanese PB-DLBCL patients and review the literature on PB-DLBCL. Methods: Thirty-one PB-DLBCL patients diagnosed between 2000 and 2021 were retrospectively enrolled for analysis. Results: The median age was 49 (range 26-79) years. The complete remission (CR) rate was 90.3%. Nine (90%) of the ten patients who experienced relapse had CNS involvement at the time of relapse. The one-year, two-year, and five-year progression-free survival (PFS) rates were 86.6% (95% confidence interval [CI] 75.2-99.8), 75.8% (95% CI 61.6-93.2), and 45.1% (95% CI 29.5-68.9), respectively. The five-year overall survival (OS) rate was 64.1% (95 % CI 48.4-85.0). A stage-modified International Prognostic Index (mIPI) less than two (five-year PFS rate 52.5% vs. 17.1%, P = 0.02) and the achievement of CR after first-line treatment (two-year PFS rate 80.3% vs. 33.3%, P < 0.001) were significant favorable prognostic factors for PFS. Hematopoietic stem cell transplantation (HSCT) after the first relapse was associated with significantly improved post-relapse OS (five-year OS rate 85.7% vs. 20.0%, P = 0.02) and PFS (five-year PFS rate 85.7% vs. 20.0%, P = 0.02). Conclusion: Patients with low-risk mIPI scores, CR after first-line treatment, and those who underwent HSCT after the first relapse had significantly better survival. Intrathecal chemotherapy conferred no benefit in preventing CNS relapse. Further research is needed to assess frontline HSCT's effectiveness in improving outcomes and preventing CNS relapses in PB-DLBCL patients.