Lobular carcinoma of the breast in situ and infiltrating.

Lobular carcinoma in situ, while histologically delineated almost 35 years ago, is still being diagnosed and reported with differing qualitative and quantitative criteria. It is important to recognize this lesion because of its frequent bilaterality and risk of developing infiltrating carcinoma in the affected breast. Because of the apparent morphologic identity of the cell of ALH and the cell of LCIS, because both are associated with some increased risk of developing carcinoma, and because both have an increased propensity to be found simultaneously with carcinoma--especially lobular carcinoma--we believe these lesions should be looked upon as basically identical. Beginning with Ewing's astute intuition nearly 60 years ago18 and culminating with the 1967 report of McDivitt and others,50 pathologists and surgeons have gradually become aware of the long-term risk associated with this nonobligatorily, premalignant lesion (LCIS). As further studies have become available, it is clear that a large majority of women with lobular carcinoma in situ or atypical lobular hyperplasia retaining the involved breast will not develop infiltrating carcinoma. However, there is an increased risk of roughly 1 percent per year. Because of the increased risk, we believe that a meticulous long-term followup is mandatory, and suggest a physical examination every two to three months for the first few years supplemented with yearly mammography (as is now being done at Memorial Hospital for patients with atypical breast lesions6). With such a followup, we believe the mortality should fall well below 5 percent in a 20-year followup, and believe this is a risk that may be acceptable to the patient and her surgeon. The boundaries of the morphologic changes acceptable as ILC have been difficult for many pathologists (including ourselves) to delineate. This is borne out by widely varying incidence figures and is due, at least in part, to the frequent admixture of ILC with poorly differentiated duct carcinoma as well as problems in deciding how large and pleomorphic the cell nuclei may be, and still be designated as lobular in origin. We believe that about 4 to 6 percent of all breast carcinomas are infiltrating lobular, and incidence rates widely divergent from this should be scrutinized carefully. Prognostically, ILC behaves similarly to poorly differentiated duct carcinomas except for some increased risk of subsequent contralateral carcinoma. Future study of lobular disease should be directed toward its histogenesis, long-term risk, and the relative success of different treatment modalities. Hormonal studies and cell culture with chromosomal analysis might shed some light on the mechanism of what may be postmenopausal regression of LCIS.