Phyllodes tumour of the breast

Phyllodes tumours are fibroepithelial tumours in which the stroma, not the epithelium, is the neoplastic component; the epithelium is stretched into the leaf-like clefts that give the name. The World Health Organization grades them benign, borderline or malignant on stromal cellularity, nuclear atypia, mitotic count, stromal overgrowth and the character of the border, and most are benign. They present as a smooth, mobile, often large lump that has grown quickly over months, in women a decade older than those with fibroadenoma. Imaging cannot reliably separate the two, and a core biopsy often returns only a fibroepithelial lesion, so any rapidly growing or large fibroepithelial lesion is excised for diagnosis. Benign phyllodes tumours and fibroadenomas share MED12 mutations, and TERT promoter mutations accumulate in borderline and malignant tumours.

Surgery is the treatment for every grade. Wide local excision with clear margins is the aim, and mastectomy is reserved for tumours too large for the breast; the traditional demand for a 1 cm margin has softened, and guidelines now accept any negative margin for benign tumours while recommending re-excision for positive margins in borderline and malignant disease. Lymph node metastases are rare, so sentinel node biopsy and axillary dissection are not performed. Adjuvant radiotherapy has no randomised evidence: a single-arm phase 2 study of 46 borderline and malignant tumours treated with margin-negative breast-conserving surgery and radiotherapy reported no local recurrences, and guidelines list radiotherapy as a consideration after breast conservation for these grades. Adjuvant chemotherapy has no proven benefit and hormone receptors, though often present in the epithelium, do not guide treatment.

Benign tumours are cured by excision and recur locally in a minority, often at a higher grade than the original. Malignant tumours recur locally more often and a substantial minority metastasise, most often to the lungs and bone within the first few years, at which point they are treated like soft-tissue sarcomas with doxorubicin-based chemotherapy and have a poor outlook. Follow-up with examination and imaging for the first few years catches most recurrences. The rarity of the disease means margin width, the role of radiotherapy and the value of molecular grading rest on retrospective series and registries rather than trials.