Ductal carcinoma in situ (intraductal carcinoma) most commonly presents as microcalcifications on screening mammography; however, it may present as a mass or with nipple discharge. Because this cancer is confined to the ductal system and does not invade the basement membrane, there is no access to either lymphatic channels or nodes. Diagnosis is made by an image-guided biopsy in which a core of tissue is interpreted by a histopathologist. Wide excision of the area of ductal carcinoma in situ is the preferred therapy for smaller lesions, though obtaining tumor-free margins is often difficult because of the diffuse nature of the disease. Adjuvant irradiation to the remaining ipsilateral breast significantly lowers the risk of later ipsilateral invasive breast carcinoma.

Carcinoma of the breast is the most common invasive cancer in women and occurs with a 2½ times greater incidence than either colorectal or lung cancer. The risk of a woman in the USA developing breast cancer during her lifetime is about 10%. The surgical treatment of breast cancer has changed considerably since 1980, with a much greater emphasis on selective therapy. Patients with stage I (less than 2 cm) or smaller stage II (less than 4 cm) carcinomas diagnosed by fine needle aspiration or image-guided biopsy are treated most frequently with lumpectomy or quadrantectomy, sentinel lymph node biopsy (followed by formal axillary lymph node dissection if node contains metastatic cancer), and postoperative radiotherapy with 50 Gy (5000 rad).