Phyllodes tumor of the breast is distinguished from fibroadenoma by which histological feature?
- A Presence of epithelial hyperplasia within the fibrous stroma
- B Calcification within the stroma on mammography (Haagensen calcification)
- C Hypercellular, mitotically active stroma with leaf-like epithelium-lined clefts and stromal overgrowth ✓
- D Bilateral occurrence and association with BRCA1 mutations
Correct answer: C. Hypercellular, mitotically active stroma with leaf-like epithelium-lined clefts and stromal overgrowth
Explanation
Phyllodes tumor (cystosarcoma phyllodes) differs from fibroadenoma by having a hypercellular stroma with stromal overgrowth, increased mitoses, and leaf-like projections of stroma lined by epithelium into cystic spaces. Fibroadenoma has a paucicellular stroma without significant mitotic activity. Malignant phyllodes has stromal sarcomatous transformation and permeative borders.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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