Mucinous subtype of invasive ductal carcinoma arising within a fibroadenoma

Fibroadenoma is a common benign tumor observed during the second and third decades of life. Malignancy transformation in the epithelial component of a fibroadenoma is rare and can occur 20 years after its diagnosis. Mammographic findings in this phenomenon include indistinct margins and microcalcifications. Here we present a 58-year-old woman with a mobile, lateral upper quadrant mass that was rather firm when palpated. The mammography showed a lobulated mass without calcification suggestive of a benign process, most probably fibroadenoma. However the excisional biopsy contained both an intracanalicular fibroadenoma and invasive ductal carcinoma with mucinous components.