Is Ductal Carcinoma In Situ a Precursor or Low‐Risk Variant of Invasive Breast Cancer? A Population Perspective

Ductal carcinoma in situ (DCIS) is usually detected with mammography screening and assumed to be a precursor of invasive ductal cancer (IDC) of the breast. Yet, despite an approximately 10-fold increase in the rate of DCIS detection and treatment within 20 years following implementation of mammography screening in the United States, IDC incidence rates remained comparatively stable (a 1.6-fold increase during the same time period). Moreover, if we accept the assumption that DCIS is a nonobligate precursor of IDC, with estimates that up to 40% may progress to IDC, then DCIS annual incidence should be at least 2.5-fold greater than that of IDC, and at least 9-fold greater than what is now reported. Such a vast underestimation of DCIS incidence seems unlikely, as over 85% of all DCIS lesions contain microcalcifications and most should therefore be detectable with modern breast screening technology. In this special report, we discuss evidence derived from population-based registries suggesting that DCIS is not a precursor but rather a low-risk variant of invasive breast cancer, with a 3.3% risk of breast cancer death over a 20-year period. A large DCIS treatment trial with a mortality endpoint is needed to bolster support for this alternative hypothesis and potentially justify treating DCIS as a low-risk systemic disease.