Risk of invasive cancer in women with lobular carcinoma in situ of the breast.

100 women underwent wide resection for palpable or mammographically detected breast lesions (1 woman had bilateral lesions). Histology excluded invasive cancer, but one or more foci of lobular carcinoma in situ (LCIS) were observed. There have been no recurrences in the 20 women who underwent total mastectomy. In the 12 patients who had a subsequent wide excision and the 68 who received no other treatment 5 presented with an invasive cancer in the same breast at some distance from the LCIS site (median follow-up 58 months). The (observed/expected) rate per 1000 per year is 10.3 for an untreated LCIS. LCIS is therefore a risk factor for invasive carcinoma. Nevertheless this risk does not indicate the use of mutilating procedures and a wait-and-see policy is appropriate.