Question
Phyllodes tumor
Answer
Phyllodes tumour is a fibroepithelial breast neoplasm, related to but distinct from fibroadenoma, arising from the intralobular/periductal stroma.
Gross: Typically larger than fibroadenoma, well-circumscribed, bosselated (lobulated) mass with a characteristic leaf-like (“phyllodes” = leaf-like in Greek) pattern of clefts and cystic spaces on the cut surface.
Microscopy:
- Leaf-like papillary projections of hypercellular stroma covered by epithelium, projecting into cystic spaces.
- The stromal component is the neoplastic element (unlike fibroadenoma, where both epithelium and stroma are typically considered polyclonal/reactive) — hence classified by stromal features.
- Graded as benign, borderline, or malignant based on stromal cellularity, nuclear atypia, mitotic activity, and the nature of the tumour margin (pushing vs. infiltrative).
Behaviour: Even benign phyllodes tumours have a tendency to recur locally if incompletely excised (given the propensity for the stroma to extend beyond the apparent margin); malignant phyllodes tumours can metastasize haematogenously (stromal component only — epithelium does not metastasize).
Treatment: Wide local excision with clear margins (rather than simple enucleation, to reduce local recurrence).