Ductal carcinoma in situ (DCIS) of the breast is defined by the proliferation of cancer cells within a galactophoric duct without these cells protruding beyond the wall of the duct, to spread to the rest of the breast.
It is essentially of mammographic finding, in fact 90% of women diagnosed with DCIS (ductal carcinoma in situ) had microcalcifications at mammography. In their vast majority, these lesions do not threaten women's lives if they are not detected, their prognosis is very good, survival at 10 years, the mostly used measure by the health authorities, is over 95%. There are the ductal form and the lobular form, the latter considered to be rather a risk factor for breast cancer. DCIS largely contribute to overdiagnosis. Tests and studies indicate that the increasing detection of DCIS has not led to the reduction of breast cancer mortality. Before the era of screening, DCIS accounted for less than 5% of all breast cancers, rising to 15-20% in all countries where screening campaigns are taking place. They are not included in the incidence figures (rate of new cases) reported by the National Cancer Institute, as they are considered separately, and not as "real" cancers. In addition, there is a lack of real consensus among pathologists regarding the classification of these lesions when analyzing the biopsies they receive, with a tendency to overclassify them into more unfavorable prognosis categories, due to the fear of underestimating a "disease".
Most DCIS are considered as non-mandatory precursor lesions toward invasive cancer; paradoxically, the spectacular increase in their detection and their subsequent surgical excision has not been followed by a proportional decrease in the incidence of invasive cancers. The major problem is that these particular entities of breast cancer are treated with the same severity as breast cancer.
In November 2016, a study conducted by University of Toronto concluded the following:
- Their treatment makes no difference to women's survival. - Women with DCIS are heavily treated (sometimes by bilateral mastectomy) and have the same probability of dying from breast cancer as women in the general population.
- Preventing recurrences by radiotherapy or mastectomy would therefore not reduce the risk of breast cancer mortality.
Similarly, our study of mastectomies in France found a steady increase in surgical procedures, our first hypothesis being the overtreatment of lesions that are not invasive cancers, but rather so-called pre-cancerous lesions and DCIS  .
The long-term consequences of over-treatment can place women's lives at risk. Radiation therapy for these lesions, for example, appears to be ineffective in reducing the risk of death from breast cancer, but it is associated with a dose-dependent increase (from 10 to 100% over 20 years) in the rate of major coronary events .
Moreover, in several countries clinical trials are being conducted to test simple active surveillance, particularly for low-grade CIS, rather than aggressive treatment:
For Philippe Autier , of the International Prevention Research Institute (IPRI), the problem is definitely inherent to routine mammography, in particular to digital mammography, which is too efficient in detecting small calcifications; these are the most frequent radiological sign of these forms, and mammography has an excellent sensitivity for the detection of these microcalcifications.
 SC Darby, M. Ewertz, P. McGale, AM Bennet, U. Blom-Goldman, D. Bronnum, et al.
Risk of Ischemic Heart Disease in Women after Radiotherapy for Breast Cancer
N Engl J Med, 368 (11) (2013), p. 987-998
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