High-Grade Surface Osteosarcoma

The grade matters because the surface, or juxtacortical, osteosarcomas are three distinct entities of differing grade that behave very differently and are treated differently. The parosteal osteosarcoma is low-grade, the commonest, classically a stuck-on ossified mass on the posterior distal femur, with the best prognosis, and is treated by wide resection alone unless it has dedifferentiated. The periosteal osteosarcoma is intermediate-grade and chondroblastic, typically diaphyseal, and is treated by wide resection often with chemotherapy. The high-grade surface osteosarcoma is the rarest and, although it arises on the bone surface, it behaves like a conventional intramedullary osteosarcoma, with the same aggressive behaviour and metastatic potential. So the grade, established on a properly planned biopsy read at a sarcoma centre, determines whether systemic chemotherapy is needed. For a high-grade surface variant I would manage it as I would conventional high-grade osteosarcoma: full staging with local MRI and chest CT, then neoadjuvant chemotherapy followed by wide resection with clear margins - limb salvage where feasible, otherwise amputation - and adjuvant chemotherapy, all within a specialist sarcoma multidisciplinary team. The key error to avoid is under-treating it as if it were a benign surface lesion or a low-grade parosteal tumour.