Phyllodes tumour is a rare tumour of the breast constituting less than 1% of all breast tumours. Malignant Phyllodes Tumour (MPT) accounts for only 10-30% of all phyllodes tumours. Heterologous sarcomatous differentiation in a MPT is an infrequent phenomenon, with the cases reported showing differentiation mostly towards liposarcoma, fibrosarcoma, angiosarcoma, osteosarcoma, or chondrosarcoma. MPTs with rhabdomyosarcomatous differentiation are scarcely seen with only three confirmed cases documented till date to the best of the knowledge after a thorough search of literature. Here, authors present a case of 45-year-old female who presented with a well-defined rapidly growing lump in the right breast for last one year. A core needle biopsy performed showed a sarcomatous picture on histology. Complete excision was subsequently done. On microscopy, most of the areas showed fibrosarcomatous changes with frequent mitoses. Some of the foci showed large pleomorphic cells in diffuse sheets that were polygonal with densely abundant eosinophilic cytoplasm and vesicular nucleus with prominent nucleoli (rhabdomyoblasts). Myogenin was diffusely positive on Immunohistochemistry (IHC). A diagnosis of MPT with rhabdomyosarcomatous differentiation was made. This case is reported here for its unusual presentation and to make pathologists aware of this rare heterologous differentiation of MPT.
57P Therapeutic vulnerability of malignant phyllodes tumour to pazopanib identified through a novel patient-derived xenograft and cell line model
