Adenoid cystic carcinoma arising in a fibroadenoma.

Adenoid cystic carcinoma (ACC) of the breast is a rare neoplasm, accounting for only 0.1 % of all breast carcinomas. An intriguing factor of ACC in the breast is its good prognosis compared to ACC in other locations, mainly in the minor salivary glands. The incidence of axillary lymph node involvement is also very low compared to that of other breast tumors, and distant metastases are uncommon. We report the case of a 65-year-old woman with a 2-year history of a well-circumscribed breast nodule sonographically thought to be a lymph node which was later excised because of rapid growth. Histologic examination showed an adenoid cystic carcinoma with squamous differentiation originating in a fibroadenoma. A review of the literature reveals no previous report of such a case.