"Benign," metastasizing adenomyoepithelioma of the breast: a report of 2 cases.

Adenomyoepitheliomas of the breast are rare tumors composed of a proliferation of 2 cell populations. For the most part, they are considered to be benign, but they locally recur. Those neoplasms that metastasize are deemed to have come from a histologically malignant primary tumor. Herein, we describe 2 cases of metastases of histologically "benign" adenomyoepitheliomas of the breast to the lung. In both cases, the primary neoplasms and the metastases did not show histologic features of malignancy. These unique cases represent another example of neoplasms that can metastasize in the absence of histologic features that would suggest malignant behavior. Establishing the diagnosis, determining optimal therapy, and predicting outcome are problematic because of the rarity of this entity. Perhaps, classification of adenomyoepitheliomas should be changed to recognize those neoplasms with malignant behavior.