Phyllodes Tumour

Relationship to fibroadenoma: There's a spectrum from fibroadenoma → cellular fibroadenoma → benign phyllodes → borderline → malignant phyllodes. Whether phyllodes actually arises from a pre-existing fibroadenoma or de novo is debated — some share clonal mutations (e.g. MED12 mutations are common to both), suggesting a subset may represent progression. Clinically, the classic scenario is a longstanding stable lump that suddenly starts growing rapidly, or a "fibroadenoma" in a woman over 40.

Rapid growth is the key clinical discriminator.

Prognosis: Benign and borderline — excellent with adequate surgery. Malignant phyllodes with metastatic disease has a poor prognosis because it behaves like a soft tissue sarcoma and responds poorly to conventional breast cancer chemotherapy. Doxorubicin/ifosfamide (sarcoma regimens) are used, but response rates are limited. Radiotherapy may reduce local recurrence for borderline/malignant cases with close margins, though evidence is limited.