Invasive Micropapillary Carcinoma in Axillary Ectopic Breast and Synchronous Ductal Carcinoma In Situ in the Contralateral Breast.

The development of ectopic breast tissue is attributable to the failure of primitive mammary tissue to regress after the development of the mammary ridge, except at pectoral breast sites, and is most often evident in the axillae. Several benign and malignant breast diseases have been reported in ectopic axillary breast tissues. The most common cancerous pathology of ectopic breast tissue is invasive ductal carcinoma. Ectopic breast cancer presenting with simultaneous primary cancer of the pectoral breast is extremely rare. Herein, we report an invasive micropapillary carcinoma of an axillary ectopic breast, combined with a synchronous ductal carcinoma in situ in the contralateral pectoral breast of a 61-year-old woman.