A 32-year-old woman with a phyllodes tumor of the breast. Histological features include stromal overgrowth, marked stromal cellularity with > 10 mitoses/10 HPF, and infiltrative margins. This would be classified as:

• A Borderline phyllodes tumor — intermediate features
• B Benign phyllodes tumor — pushing margins, mild stromal atypia
• C Malignant phyllodes tumor — with high mitotic rate, stromal overgrowth, and infiltrating borders ✓
• D Fibroadenoma — intracanalicular pattern without stromal overgrowth

Explanation

WHO criteria for malignant phyllodes tumor require: stromal overgrowth (stromal elements without epithelium in at least one low-power field), marked stromal hypercellularity and atypia, and ≥10 mitoses/10 HPF, with infiltrative (not pushing) tumor margins. Borderline has 5–9 mitoses/10 HPF with moderate atypia. Benign phyllodes has <5 mitoses/10 HPF, mild atypia, and pushing margins. Fibroadenoma lacks leaf-like clefts and hypercellular stroma.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.