Breast localizations of cancers of extramammary origin are infrequent. They represent for 0.5 to 6.6% of all breast cancers and affect mostly women. We report an exceptional case of secondary breast localization of a tumor for a man.This is a 74 year old man who presented a retro-areolar mass. Mammary scan found a suspect and bilateral axillary adenopathies. The histological study of the mammary biopsy performed revealed a monomorphic malignant tumor proliferation of round cells. The immunohistochemical study showed cytoplasmic expression of the tumor cells of the anti-CD138 antibody, CD79a and anti-kappa light chain. The examination and bone marrow biopsy made it possible to make the diagnosis of mammary localization of a multiple myeloma with a light chain kappa. The extramedullary sites of the MM are uncommun and are found exceptionally in the breast and even more in a man.