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

ABSTRACT

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.