Lobular carcinoma in situ of the breast.

Lobular carcinoma in situ (LCIS) of the breast is commonly identified as an incidental finding in breast biopsies performed because of either a mammographic abnormality or a palpable mass. Although long recognized as an entity, the significance and optimal treatment of LCIS remains controversial. Initially regarded as a pre-invasive form of breast cancer analogous to ductal carcinoma in situ (DCIS), LCIS was treated by mastectomy. As evidence mounted for an equal risk of invasive carcinoma in both breasts, bilateral mastectomy was advocated by some. More recent studies suggest that LCIS is a marker for increased risk rather than a true precursor of invasive carcinoma, and this allows a more conservative approach. The pathologic aspects and natural history of LCIS are discussed.