[Breast cancer: apropos of "in situ"].

Since the introduction of screening mammography, the proportion of ductal carcinoma in situ (DCIS) has significantly increased. Their early detection result in the majority of the cases in an exclusive radiologic expression and a histopathologic measure inferior to 20 mm. Newly formulated proposals of histologic classifications may permit in the future to identify subtypes of DCIS with a different clinical behaviour and prognosis. In analogy to the treatment's evolution for invasive mammary cancers, the concept of conservative breast surgery is evaluated in prospective randomized trials, together with the impact of adjuvant radiotherapy. Preliminary results report high survival rates, despite a considerable number of local recurrences. Radiotherapy seems not to reduce proportionally the risk for non-invasive and invasive recurrences.