Basaloid type adenoid cystic carcinoma of the breast

We report a case of adenoid cystic carcinoma (ACC) of the breast with a prominent basaloid feature. The patient was a 62-year-old Japanese woman with a right breast mass, measuring 1.5 cm in diameter. Histologically, the tumor was composed of basal cell-like tumor cells, and it was originally diagnosed as invasive ductal carcinoma. The presence of PAS-positive basement membrane material around the tumor cell nests may be a diagnostic clue to ACC. The prognosis of ACC of the breast is considered to be favorable. However, basaloid type ACC may represent a poor prognosis, since our case revealed an aggressive behavior in spite of its small size.