图示小叶原位癌。小叶原位癌由末端乳腺导管与腺泡内的瘤性细胞增生形成。细胞小而圆。尽管这些病变处于低分级，在同侧或对侧乳腺有30%发展成浸润性癌的风险。 Lobular carcinoma in situ is seen here. Lobular CIS consists of a neoplastic proliferation of cells in the terminal breast ducts and acini. The cells are small and round. Though these lesions are low grade, there is a 30% risk for development of invasive carcinoma in the same or the opposite breast.