Most breast cancers arise from which anatomical area of the breast?

• A. Terminal duct lobular unit
• B. Adipose tissue
• C. Lactiferous ducts only
• D. Cooper's ligaments

Answer: (A)

Most breast cancers arise from the terminal ductal lobular unit, the functional area where ducts converge with lobules. This unit contains the ductal and lobular epithelium—the cells that line the milk ducts and lobules—and is where most malignant transformation begins. In situ cancers (like DCIS and LCIS) themselves occur within the terminal ductal lobular unit, and invasive cancers typically originate from these epithelial cells as they progress along the ductal-lobular pathways.

Adipose tissue is mainly fat and not a common site of epithelial breast cancers. The lactiferous ducts alone omit the lobular component, which is essential to where most cancers start, and Cooper's ligaments are connective tissue structures that provide support rather than being sites of malignant transformation.