Primary carcinoma of ectopic breast tissue.

We describe a case of a 37-year-old woman with a left axillary mass. Often, the initial differential diagnosis of an axillary mass is not easy to make. We performed fine-needle aspiration of the axillary mass that revealed the presence of numerous epithelial neoplastic cells. A bilateral digital mammography, chest and abdomen computed tomography scan, and a magnetic resonance imaging scan (MRI) of the axillary region were performed. In our case, the MRI was able to exclude the presence of neoplastic tissue in the breast; moreover, it confirmed the presence of metastatic lymph nodes and recognized a second type of nodular lesion in the axilla, showing on the MRI a radiologic pattern similar to breast tissue.