In recent years the diagnosis of lobular carcinoma of the breast has been made with increasing frequency. The in situ form as well as the infiltrative variety are now well-recognized, and it is clearly established that both are true cancers.1 Because there are features of lobular breast cancer which distinguish it from the common infiltrating ductal carcinoma, we suggested a therapeutic approach in 1965 when fewer than 40 patients with in situ lobular carcinoma had been reported.2 Now that the experience with almost 500 reported patients with lobular carcinoma has been reviewed,3 the natural history of the disease is well enough known to justify supporting and extending these therapeutic recommendations. Our purpose is to present the treatment regimen we are currently following. In Situ Lobular Carcinoma This neoplasm is often not a tumor in that the palpable mass for which the biopsy was undertaken proves to be