Epidemiological survey of preinvasive breast cancer.

DCIS and LCIS are different breast diseases at various points of view. DCIS has in most cases a clinical or mammographical pattern, whereas LCIS represents an incidental finding in breast tissue removed for another reason. However, DCIS found incidental to benign disease may be a more innocuous form of tumour. Multifocal foci are more frequent in LCIS than in DCIS, but microinvasion and coexisting unsuspected infiltration carcinoma are more often found in DCIS. Contralateral in situ breast carcinoma is a rare event in DCIS. It is seldom found in LCIS. The risk of development of an infiltrating ipsilateral carcinoma after biopsy or excision showing in situ carcinoma is higher for DCIS than for LCIS. However, in most cases the invasive tumour occurs at or near the site of the original biopsy. Among LCIS patients, invasive carcinoma occurs anywhere in the breast parenchyma. The risk of development of contralateral invasive cancer is very low in DCIS patients, but it is high in LCIS patients. It may be lobular, ductal or a mixture of different types. DCIS has to be considered as a truly preinvasive lesion although LCIS is rather a marker of increased risk.