AbstractThe case histories of all patients with osteosarcoma of the trunk entered into the consecutive studies COSS 80 through COSS 86 of the Cooperative German/Austrian Osteosarcoma Study Group (COSS) were analyzed in order to evaluate their clinical characteristics and the impact of modern neoadjuvant therapy on prognosis. They were compared to those of all patients with extremity osteosarcoma treated according to the same protocols. While tumors of the trunk comprised only 32 (4.8%) of 665 primary classical osteosarcomas, secondary osteosarcomas were much more likely to be located in bones of the axial skeleton (6 of 18, 33%). Patients with primary osteosarcoma of the axial skeleton were older (mean: 20.8 vs. 15.2 years,P<0.01) and were more likely to present with metastases at diagnosis (34% vs 12%,P<0.001) than those with primary extremity osteosarcoma.In contrast to extremity tumors, local surgical treatment failure was very common in osteosarcomas of the trunk. Complete tumor removal was achieved in less than half of all evaluable cases. The prognosis of eight patients with localized primary axial osteosarcoma and effective surgical local control was not inferior to that of 483 equally evaluable patients with extremity tumors.In conclusion, while secondary systemic spread of axial osteosarcoma may be avoided in patients treated with multiagent chemotherapy, successful treatment is often barred by primary metastatic disease and inability to control the local tumor site. © 1995 Wiley‐Liss, I