Benign Epithelial Proliferations and Precursor Lesions

Overview: The Three Groups

1. Nonproliferative Breast Changes (Fibrocystic Changes) - MAIN FOCUS

A. Cystic Change (with Apocrine Metaplasia)

• Small cysts form by dilation of lobules, which may coalesce into larger cysts
• Unopened cysts contain turbid, semitranslucent brown- or blue-colored fluid (called "blue-dome cysts")
• Cysts are lined by either flattened atrophic epithelium or metaplastic apocrine cells
• Apocrine cells have abundant granular eosinophilic cytoplasm resembling normal apocrine sweat gland epithelium
• Calcifications are common - they form on secretory debris and appear as clustered rounded densities on mammography
• Solitary, firm cysts may raise concern for malignancy; the diagnosis is confirmed by disappearance of the mass after fine-needle aspiration

B. Fibrosis

• Cysts frequently rupture, releasing secretory material into the adjacent stroma
• This triggers chronic inflammation and resultant stromal fibrosis
• The fibrosis produces the palpable nodularity characteristic of fibrocystic disease
• This is the "fibro-" component of the term "fibrocystic"

C. Adenosis

• Defined as an increase in the number of acini per lobule
• Acini are lined by columnar epithelial cells
• Calcifications are occasionally present within the lumens
• This is a lobular enlargement without compression or distortion (distinguishing it from sclerosing adenosis, which is proliferative)

Additional Nonproliferative Change: Lactational Adenoma

• Presents as a palpable mass in pregnant or lactating females
• Consists of normal-appearing breast tissue with lactational changes
• Regresses after cessation of breastfeeding
• Thought to be an exaggerated local response to gestational hormones rather than a true neoplasm

2. Proliferative Breast Disease Without Atypia

• Usual ductal hyperplasia (UDH): Increased number of both luminal and myoepithelial cells filling and distending ducts and lobules. Irregular lumens often visible at the periphery of cellular masses. Typically an incidental finding.
• Sclerosing adenosis: Glandular proliferation with increased acini, compressed and distorted by stromal fibrosis. The compression can create solid cords or double strands of cells in dense stroma - can mimic invasive carcinoma. May present as palpable mass, radiologic density, or calcifications.
• Radial scar (radial sclerosing lesion): Small stellate lesion that closely mimics invasive carcinoma mammographically, grossly, and histologically. Has a fibroelastic core with radiating ducts/lobules that show hyperplastic changes.
• Papillomas: Benign epithelial growths within ducts, often causing nipple discharge.
• Fibroadenoma with complex features: Mixed stromal and epithelial proliferation.

3. Proliferative Breast Disease With Atypia (Atypical Hyperplasia)

• A duct is partially (not completely) involved by an atypical epithelial proliferation
• Comprises rounded, cytologically monotonous cells with interspersed cribriform spaces
• Shares features with low-grade DCIS but falls short of full criteria (too small, or only partial duct involvement)

• A population of monomorphic small, round, loosely cohesive cells partially fills a lobule
• Shares cytologic features with lobular carcinoma in situ (LCIS) but does not completely fill/distend the lobule

Clinical Significance Summary

• Most benign epithelial proliferations do not cause symptoms - found as mammographic calcifications/densities or incidentally
• The majority are not precursors of cancer directly
• These lesions predict risk in either breast, not just the affected breast
• Risk reduction can be achieved by surgery or chemoprevention (e.g., tamoxifen for ADH/ALH), but most affected women undergo surveillance rather than surgery since most will not develop cancer
• Fibrocystic changes alone (nonproliferative) carry no excess cancer risk