15-year-old boy, pain and swelling in the knee area. An X-ray shows osteolytic patches in the distal femur metaphyses with periosteal reaction. S
- Distinct reduction of cell density after undergone neo-adjuvant chemotherapy
- Regressive changes of tumour tissue with fibrosis and increased polymorphism of residual cells with unchanged tumour osteoid (compare with previous bone trabeculae)
Evidence of osteoid formation is crucial for diagnosis, even if another intercellular substance such as cartilage, chondroosetoid or collagen is evident. Histologically osteoblastic, chondroblastic and fibroblastic osteosarcoma can be distinguished (they can occur in different areas of one tumour). The histological estimation of tumour tissue vitality after undergone chemotherapy has important therapeutic and prognostic consequences.