Carcinoma of supernumerary breast of vulva with bilateral mammary cancer.

Primary mammary cancer often develops at multiple sites in either one or both breasts, evidently the result of a common carcinogen acting in multicentric loci. The occurrence of carcinoma in accessory breast tissue has been recorded, including carcinoma in supernumerary breast tissue within the labium, although the latter is rare. A 62-year-old woman developed carcinoma of the right breast which was followed nearly five and one half years later by the occurrence of adenocarcinoma in supernumerary breast tissue within the left labium majus. Concomitantly, carcinoma was detected in the left breast. The three cancers exhibited histologic features compatible with primary rather than metastatic lesions. The development of primary carcinoma in both breasts as well as within ectopic mammary tissue in the labium appears to be the first recorded instance of such an event.