9020/3 Phyllodes tumor, malignant
SynonymsCystosarcoma phyllodes, malignant
|ICD-O-3 topography code:||C50|
Phyllodes tumours constitute one of the two major categories of fibroepithelial tumours of the breast (the other being fibroadenomas). Fibroepithelial breast tumours are biphasic lesions composed of an epithelial and a mesenchymal (stromal) component. The latter is quantitatively predominant and determines the overall appearance of the lesion.
Malignant PTs are diagnosed when the tumour shows a combination of marked nuclear pleomorphism of stromal cells, stromal overgrowth defined as absence of epithelial elements in one low-power microscopic field containing only stroma, increased mitoses (> 10 per 10 HPF), increased stromal cellularity which is usually diffuse, and infiltrative borders. Malignant PTs are also diagnosed when malignant heterologous elements are present even in the absence of other features. Owing to overgrowth of sarcomatous components, the epithelial component may only be identified after examining multiple sections with diligent sampling of the tumour.
See Phyllodes tumour for images and detailed discussion.