Pigmented axillary nodule:: Carcinoma of an ectopic axillary breast

BACKGROUND. Ectopic mammary tissue appears in humans owing to an incomplete embryologic regression of the mammary ridges. The same pathology that affects normally positioned breasts, including carcinoma, can occur in ectopic mammary tissue. OBJECTIVE. The objective was to present the case of a 43-year-old woman who developed a ductal mammary carcinoma of ectopic breast tissue. METHODS. We describe the patient's history, the histologic diagnosis, and the therapy carried out. We also discuss the clinical differential diagnosis and current management options. RESULTS. The patient developed a ductal mammary carcinoma in the axilla, which is the most common site for the occurrence of carcinoma of ectopic breast tissue. She has been sucessfully treated with surgery, lymphadenectomy, radiotherapy, and chemotherapy. Accessory mammary tissue is a relatively frequent incidental finding, whereas carcinoma of ectopic tissue is very rare. CONCLUSIONS. Carcinoma occurring in ectopic breast tissue remains rare, but this diagnosis must be suspected when confronted with any axillary nodule. The prognosis is similar to carcinoma of normal breast in the same tumor, node, metastasis stage, although it has a higher rate of lymph node involvement. There is no consensus on the advisability of excising ectopic mammary tissue.