Ductal carcinoma in situ (DCIS) is a lesion that occurs when the cells lining the milk ducts of the breast become malignant/cancerous but are confined to the basement membrane of the duct and have not spread into the surrounding breast tissues.  • DCIS represents 20–25% of new breast cancer cases (National Institute of Health).  • Cases of DCIS have increased exponentially with the increased uptake of screening mammography.  • Without definitive management, approximately 20–30% of DCIS cases will progress to invasive breast cancer.  • Unlike lobular carcinoma in situ (LCIS), DCIS is NOT a premalignant lesion, but is non-invasive breast cancer/early-stage breast cancer.  • These lesions are typically found during routine screening mammography and most often present as branching, heterogeneous, clustered and/or pleomorphic microcalcifications.  • Traditional ways of classifying DCIS pathologically (comedo, cribriform, solid, micropapillary, or papillary) are becoming less common with newer systems classifying DCIS on the basis of nuclear grade and necrosis. DCIS is usually classified as low-, intermediate-, or high-grade.  • With any breast concern, ensure that your breast examination evaluates both breasts, both axillae, and the other lymph node basins (cervical, supraclavicular, infraclavicular).