Malignant Round Cell Tumours of Bone

Malignant round cell tumours are high-grade tumours with scanty cytoplasm and hyperchromatic nuclei. Morphological subtyping requires ancillary techniques like immunohistochemistry, FISH or molecular studies. The entities in this group are undifferentiated round cell sarcomas, lymphoblastic/Burkitt lymphoma, small cell osteosarcoma, mesenchymal chondrosarcoma, metastatic neuroblastoma and rare entities like desmoplastic small round cell tumour. In this chapter, the undifferentiated round cell sarcomas of bone and soft tissue and its differentiation from other round cell tumours of bone are mainly discussed. Metastatic neuroblastoma, a common tumour of children, is also included.