Recent developments in the histological diagnosis of spindle cell carcinoma, fibromatosis and phyllodes tumour of the breast

This article reviews recent advances in the diagnosis of these three unusual tumours of the breast. Spindle cell carcinoma needs to be considered in the differential diagnosis of many mammary spindle cell lesions: it is important to be aware of the wide range of appearances, including the recently described fibromatosis-like variant. Immunohistochemistry using a broad panel of cytokeratin antibodies is needed to exclude spindle cell carcinoma; there is frequent expression of basal cytokeratins and p63. CD34 is often expressed by the stroma of phyllodes tumours, but does not appear to be expressed by spindle cell carcinoma or fibromatosis. Nuclear beta-catenin is found in about 80% of fibromatoses, but can also be seen in spindle cell carcinomas and phyllodes tumours. Two recent studies have described features useful in the distinction of phyllodes tumour and fibroadenoma on core biopsy, including increased cellularity, mitoses and overgrowth of the stroma, adipose tissue in the stroma and fragmentation of the biopsy specimen. Periductal stromal tumour is a recently described biphasic tumour composed of spindle cells around open tubules or ducts (but no leaf-like architecture) with frequent CD34 expression. The overlap of morphology with phyllodes tumour suggests that it may be best regarded as a variant of phyllodes tumour.