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Matched‐pair analysis comparing the outcomes of primary breast and nodal diffuse large B‐cell lymphoma in patients treated with rituximab plus chemotherapy

Primary breast diffuse large B‐cell lymphoma (DLBCL) is an extremely rare presentation of non‐Hodgkin's lymphoma that has been associated with poorer clinical outcomes compared with nodal DLBCL in the pre‐rituximab era. The aim of this study was to investigate the impact of rituximab on clinical outcomes in patients with primary breast DLBCL. Data from 25 female patients with primary breast DLBCL receiving rituximab plus chemotherapy were matched to 75 female patients (1:3) with nodal DLBCL by following five established prognostic factors (age, Ann Arbor stage, Eastern Cooperative Oncology Group performance status, serum lactate dehydrogenase level and B symptoms). Overall survival (OS) was similar between primary breast and nodal DLBCL groups (3‐year OS rate, 82.2% vs. 90.7%, respectively; p = 0.345). In the analysis of immunohistochemically defined prognostic subgroups, 19 of 20 available cases in the primary breast DLBCL group displayed a non‐germinal center (GC) phenotype. Compared with patterns of recurrence, extranodal progression in the breast or central nervous system (CNS) was significantly higher in the primary breast DLBCL group than in the nodal DLBCL group (p < 0.001). Additionally, the stage‐modified International Prognostic Index was the only independent prognostic factor for OS in this population. This suggests that clinical outcomes of primary breast DLBCL might no longer be inferior to those of nodal DLBCL in the rituximab era, which might be associated with the intrinsic biologic characteristics of the non‐GC phenotype. However, despite including rituximab, extranodal progression in the breast or CNS was problematic. This study was registered at www.clinicaltrials.gov as no. NCT01266668.