Which of the following breast lesions are noninvasive malignancies?

A. Intraductal carcinoma of the comedo type.

DISCUSSION: Tubular, mucinous, and medullary carcinomas are histologic variants of infiltrating ductal cancer and are all invasive malignancies. Infiltrating lobular cancer is a particular histologic variant of invasive breast cancer characterized by permeation of the stroma with small cells that resemble those found in the breast lobule or acinus. Intraductal carcinoma refers to a malignancy of ductal origin that remains enclosed within duct structures. This noninvasive proliferation can undergo central necrosis, which frequently calcifies to form the microcalcifications seen on mammography. The central necrosis within enlarged and back-to-back ductal structures resembles comedoes and gives rise to the term “comedocarcinoma,” now reserved for this histologic variety of intraductal carcinoma.