DCIS comprises a heterogeneous group of noninvasive neoplastic proliferation with diverse morphologic appearances and risks of subsequent recurrences and development of subsequent invasive carcinoma. The tumor distends and distorts the ducts in the TDLU so that the terminal ducts enlarge and resemble large ducts. Although the tumor is confined to the TDLU, neoplastic cells can spread throughout a ductal system and produce extensive lesions involving an entire sector of a breast. DCIS occurs throughout the age range of breast carcinoma with mean age at diagnosis between 50 and 59 years, similar to the mean age of women with invasive ductal carcinoma. Mammography is a very sensitive diagnostic procedure for detecting DCIS, as a substantial proportion is not palpable.
Calcifications are frequent and produce a characteristic branching pattern on mammography.
Histologically, comedocarcinoma grows in a solid pattern with a central area of necrosis. Large pleomorphic tumor cells with irregular nuclei, commonly with prominent nucleoli characterize the tumor. The tumor spreads extensively through ducts well beyond the extent of its visible confines. Thus excision margins frequently contain tumor and the technical difficulties of ensuring complete excision frequently demand mastectomy. The tumor cells are smaller and more uniform compared to comedocarcinoma and lack necrosis.