Abstract
Malignant phyllodes tumors (MPTs) represent the most pernicious type of intralobular stromal proliferation known as a "fibroepithelial lesion" (FEL). They comprise a small fraction of breast malignancies and can present as either a pure MPT or sometimes include a heterologous component (liposarcoma, chondrosarcoma, osteosarcoma, or rhabdomyosarcoma). Of the fraction of MPTs that include heterologous components, very little about those with chondroblastic osteosarcomatous differentiation has been described in the literature. As such, a characteristic staining profile has yet to be established, even though morphological analysis is the cornerstone of diagnosis. The few reported cases have described a poor prognosis. Therefore, we present a case of MPT with chondroblastic osteosarcomatous differentiation to contribute to the dearth of literature examining this entity.