Which of the following breast lesions is considered to have the greatest potential for eventual progression to a malignant lesion?

While fibrocystic disease may have many components, including cyst formation, apocrine metaplasia (a benign alteration of cyst epithelium to resemble that of apocrine sweat glands), sclerosing adenosis, and fibrosis, only the epithelial hyperplasia (usual, atypical, or carcinoma in situ) is thought to indicate significant premalignant (or malignant, for carcinoma in situ) potential. For this reason, most pathologists pay paicular attention to the epithelial lining of the ducts and lobules when evaluating breast biopsy specimens with fibrocystic disease. Fibrocystic breasts without any evidence of epithelial changes do not appear to have any significant increased risk of progression to breast cancer. (You should, however, be aware that a fibrocystic breast may make both breast palpation and mammography more difficult and make it more likely to miss a small lesion.) Fat necrosis is seen after breast trauma, and has no significant malignant potential. Ref: Chandrasoma P., Taylor C.R. (1998). Chapter 56. The Breast. In P. Chandrasoma, C.R. Taylor (Eds), Concise Pathology, 3e.