[Primary breast diffuse large B-cell lymphoma developing subsequent to estramustine therapy for prostate cancer].

An 85-year-old male presented with 1-year history of a right breast mass. Needle biopsy of the mass revealed diffuse proliferation of large lymphoid cells that were positive for CD20, BCL2, BCL6, and MUM1 and negative for CD5, CD10, MYC, and EBER. The patient was diagnosed as having diffuse large B-cell lymphoma, a type of primary breast lymphoma (PBL). Sex hormone imbalance, which causes conditions such as gynecomastia, is associated with PBL development in males. Estramustine is a nitrogen mustard moiety linked to estradiol. For 5 years, the patient underwent estramustine therapy for treating prostate cancer. Our case suggests an important role of estrogen in PBL development.