Adenomyoepithelioma of the breast. A spectrum of biologic behavior.

Adenomyoepitheliomas of the breast have been considered to have limited metastatic potential; axillary node metastasis has been reported, but there has been no report of distant metastasis. We report six cases, including two malignant adenomyoepitheliomas, one of which metastasized to the lung and brain. Patient age ranged from 26 to 63 years (mean 46). Primary tumors were solitary and measured 0.9-3.5 cm (mean 1.7). Five of six tumors presented as palpable masses. Two patients treated by local resection have no evidence of disease at 5 and 18 months' follow-up. Two patients treated by local resection had recurrences, one at 48 the other at 60 months. The fifth patient had a spindle-cell type adenomyoepithelioma diagnosed as malignant because of high mitotic rate and cytologic atypicality of the myoepithelial component. This patient was treated by mastectomy and has no evidence of disease at 18 months. The sixth patient, initially treated by local excision, had six local recurrences over 52 months treated by reexcisions, mastectomies, and radiation. A lung metastasis was resected at 54 months and brain metastases were identified at 60 months with death occurring at 64 months. Both malignant adenomyoepitheliomas had high mitotic rates [11-14/10 high-power fields (HPF)] diffusely throughout the tumors and foci of cytologically malignant cells. The malignant adenomyoepithelioma that metastasized had an infiltrative growth pattern that increased with successive local recurrences. The four other tumors had only isolated areas of mitotic activity (maximum 1-9/10 HPF) and minimal cytologic atypia. Immunohistochemistry performed on five of six cases confirmed dual epithelial/myoepithelial cell populations in all tumors examined, including the metastasis. Electron microscopic examination of the malignant adenomyoepithelioma that metastasized also confirmed dual epithelial/myoepithelial cell populations in a local recurrence and the lung metastasis. We conclude that there is a spectrum of behavior for breast adenomyoepitheliomas with potential for local recurrence and, rarely, distant metastasis.