Papillary carcinoma arising from ectopic breast tissue in an axillary lymph node.

A cystic carcinoma was located in an axillary lymph node of a 90-year-old woman. The lymph node also contained cytologically benign mammary ducts and a few small glands that had epithelium cytologically intermediate between the normal epithelium and the neoplastic cells. In a subsequent mastectomy specimen, a small intraductal papillary carcinoma was found, differing cytologically and architectonically from the nodal carcinoma. The nodal carcinoma is considered primary because of its morphologic differences from the mammary lesion, the in situ nature of the mammary tumor, and the transition of benign to atypical epithelium in the nodal inclusions. The occurrence of two tumors is viewed as a field effect.