Improvements in mammography in the past 25 years have made it possible to detect before surgery many lesions with a high probability of being pre-invasive carcinoma. Because these cancers are virtually all cured by mastectomy, there has been considerable interest in alternative types of treatment. Retrospective studies of pre-invasive carcinoma treated by biopsy only revealed subsequent carcinoma in 30 to 40% of patients. Among women with lobular carcinoma in situ (LCIS), the frequency of subsequent carcinoma was nine times the expected rate, and mortality due to the disease was 11 times greater than expected. The risk of later invasive carcinoma appeared to involve both breasts equally when LCIS was present and to be largely limited to the breast that harbored intraductal carcinoma (IDC). When mastectomy was performed for pre-invasive carcinoma, unsuspected invasion was found in 4% of patients with LCIS and 6% with IDC.

It remains to be determined whether multicentric preinvasive carcinoma will follow the same course in patients with palpable invasive carcinoma treated by partial mastectomy and some form of adjuvant therapy. At present, it is prudent to treat pre-invasive breast cancer by ipsilateral mastectomy with low axillary dissection and to perform a contralateral breast biopsy. However, prospective, controlled investigations are urgently needed to identify groups of patients with a high or low risk of developing invasive carcinoma and to determine whether non-surgical treatment can alter the course of pre-invasive disease. By pursuing these studies, it may ultimately be possible to measure the success of breast cancer detection by the number of patients cured without mastectomy.