Objective:To investigate the clinicopathologic features

immunohistochemical foundings and prognosis ofprimarybreast diffuse large B cell lymphoma(DLBCL).Methods:Twelve cases of primary breast DLBCL

diagnosed according to the 2008 World Health Organization staging standards for haematopoietic and lymphoid tumors

were retrospectively studied.Immunochemical study was perfomed and follow-up information analyzed.The histopathologic and immunophenotypic features of all cases were summarized.Subclassification was carried out when CD10 and/or Bcl 6 positivity and negativity for MUM1 were considered indicative of germinal center B cell like type DLBCL(GCB DLBCL)and the opposite expression as non germinal center B cell like subtype(non GCB DLBCL).Results:Female 10 patients

male 2 patients.Median age of patients was 49 years.7 patients in right breast

5 patients in left.12(100%)patients in stageⅠE.The International Prognostic Index(IPI)of 1 patients was 2

which of 2 patients was 1

and which of 9 patients was 0.Follow-up information was available in 6 patients(50%)

four of which were still alive and two died(survived 7 and 19 months respectively).The patients usually presented with unilateral painless enlargement of breast.Morphologically

the lymphoma cells of 7 DLBCL cases showed a centroblastic variant

5 a immunoblastic variant.5 patients with lymphoepithelial lesions(LEL).Expression of Bcl6 and MUM1 protein was observed in 8 and 12 cases

respectively

and without expression of CD10 in 12 cases.All of 12 patients with DLBCL belong to the non GCB DLBCL.Most cases demonstrated high proliferation index

the median of Ki-67 index was 40%and more than 40%was found in 7 cases(58.3%).Conclusion:Primarybreast diffuse large B cell lymphoma is a rare entity

and shows a non germinal center B cell phenotype

accurate pathologic diagnosis relies on detailed histologic examination and immunochemical study

and treated mainly by chemotherapy combining with other therapies.