Retroperitoneal dedifferentiated liposarcoma with osteosarcomatous components: a case report.

We report a rare case of recurrent retroperitoneal dedifferentiated liposarcoma with osteosarcomatous components. An 82-year-old male diagnosed with recurrent retroperitoneal liposarcoma underwent a tumor resection. Histologically, osseous matrix with osteoid and mature hyaline cartilaginous tissues with high cellularity were observed in a fibrous background through most of the tumor, and scattered MDM2- and CDK4-positive atypical hyperchromatic stromal cells were detected surrounding the dedifferentiated areas. Dedifferentiation occurs in up to 10% of well-differentiated liposarcomas, frequently resembling a malignant fibrous histiocytoma-like pleomorphic sarcoma. In contrast, divergent differentiation with osteosarcomatous components is considered to be extremely rare.