Lobular carcinoma in situ in sclerosing adenosis. A potential source of confusion with invasive carcinoma.

A group of five different patients who had extensive sclerosing adenosis with ductules containing cells characteristic of lobular carcinoma were studied (six breasts in all). Because of the complex arrangement of ductules in sclerosing adenosis, the possibility of an invasive lobular carcinoma was considered in two cases. The distinction between sclerosing adenosis with lobular carcinoma in situ and infiltrating lobular carcinoma rests with the overall architecture of the lesion as seen at low power. Foci of sclerosing adenosis, with or without carcinoma in situ, have dilated ductules peripherally, and narrow ones centrally, whereas infiltrating lobular carcinoma has no overall organization. Because of the diagnosis of lobular carcinoma in situ, extended simple mastectomy was performed in three patients, and as expected, the lymph nodes were free of tumor.