A 24-year-old woman presents with a well-circumscribed, firm, highly mobile 2 cm breast lump that has been stable in size for two years. Excision biopsy shows a proliferation of both stroma and epithelium, with compressed ducts slit-like by the surrounding cellular myxoid stroma. There is no stromal overgrowth, atypia or mitotic activity. What is the diagnosis?

• A Tubular adenoma
• B Phyllodes tumour, benign
• C Fibroadenoma ✓
• D Intraductal papilloma

Explanation

The biphasic lesion with a pericanalicular or intracanalicular growth pattern, myxoid stroma compressing ducts into slits, absence of stromal overgrowth and low mitoses defines fibroadenoma, the commonest benign breast tumour of young women. Phyllodes tumour is the key distractor but is distinguished by greater stromal cellularity, stromal overgrowth, leaf-like fronds and higher mitotic activity. Fibroadenomas are oestrogen sensitive, may enlarge in pregnancy and are associated with mutations of MED12 in the stromal component.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.