Phyllodes tumour

Phyllodes tumour is a rare biphasic epithelial and stromal neoplasm of the breast. Most patients are in their fourth or fifth decade of life. The biological behaviour of these tumours is unpredictable, although tumour size, mitotic activity and stromal atypia are histological guidelines for assessing the biological potential. The malignant cases resemble and behave as sarcomas rather than as carcinomas.

Cytological diagnostic features

• Hypercellular smears with both epithelial and stromal components
• Phyllodes (leaf-like) stromal fragments
• Numerous spindle cells with elongated irregular nuclei and occasional nucleoli
• Fragments of metachromatically staining stroma
• Epithelial hyperplasia may be present

The cytological distinction from fibroadenoma is based mainly on the stromal nuclear features and on the cellularity of the stromal fragments. Highly cellular stromal fragments favour phyllodes tumour, in contrast with the relatively paucicellular fragments of fibroadenoma. The separation of benign from malignant phyllodes tumours is based on atypical stromal cells and mitotic features in the spindle cells adjacent to the ducts. With increasing cellularity and atypia, malignant phyllodes tumour is favoured. However, final classification should always be made on the surgical specimen.
A significant degree of epithelial proliferation may also occur in phyllodes tumours, including atypical hyperplasia which can potentially lead to a misdiagnosis of carcinoma. When atypical epithelial hyperplasia is present, cytological features suggesting a phyllodes tumour rather than a carcinoma consist of increased number of naked spindle-shaped nuclei and hypercellular stromal fragments ('phyllodes fragments').