Coexistent adenomyoepithelioma and invasive ductal carcinoma of the breast: presentation as separate tumors.

Adenomyoepitheliomas are rare breast tumors. We report an unusual case of adenomyoepithelioma associated with invasive ductal carcinoma here. Histologically, the lesion consisted of two separate tumors. One nodule corresponded to invasive ductal carcinoma consisting of tubular and trabecular arrangements of columnar or cuboidal neoplastic cells. The other tumor corresponded to adenomyoepithelioma consisting of an inner layer of neoplastic cells with basophilic cytoplasm and the outer layer of neoplastic cells with clear cytoplasm. Immunohistochemically, some myofibroblasts were observed in the stroma of both adenomyoepithelioma and invasive ductal carcinoma, but no CD34-positive stromal cells were seen in the stroma of either lesion. The stromal reaction of adenomyoepithelioma resembles that of intraductal papilloma in the previous study. To the best of our knowledge, this is the first case of coexistent adenomyoepithelioma and invasive ductal carcinoma of the breast that were discovered as separate nodules. Clinicians and pathologists should be aware of such an association because they need to distinguish such a case from malignant neoplasms arising in adenomyoepithelioma. Additionally, our preliminary report suggests that the stromal response of adenomyoepithelioma may resemble that of intraductal papilloma.