Malignant phyllodes tumor of the breast with predominant chondrosarcomatous differentiation

Malignant phyllodes tumor of the breast is a rare biphasic neoplasm, the stromal component of which may show homologous and heterologous sarcomatous elements. We present a case of a histologically malignant phyllodes tumor with sarcomatous overgrowth, affecting a 37-year-old woman in whom a chondrosarcomatous component constituted over 80% of the tumor volume. A malignant phyllodes tumor displaying a predominant chondrosarcomatous component is indeed rare, and the differential diagnosis could well affect the therapeutic approach, mainly with regard to metaplastic carcinoma and primary chondrosarcoma of the mammary gland. Thus, it is important to sample the tumor thoroughly to detect the presence of any area of typical phyllodes tumor, which could be very small. Immunohistochemical stains also should be performed so as to exclude a malignant epithelial component. After the final morphological diagnosis, our patient underwent a complete mastectomy without axillary disection. One year later, no local recurrence or metastasis was apparent.