LAUSR

Background/Aim: The diaphyses of long tubular bones are a very rare primary site of osteosarcomas and their characteristics and disease course are only poorly defined. Patients and Methods: We screened the Cooperative Osteosarcoma Study Group’s (COSS) database for eligible cases and detected 162 (130 high-grade central, 3 low-grade central, 6 high-grade surface, 17 periosteal, 6 parosteal). Tumor characteristics, treatments, and outcomes were then investigated. Results: Affected individuals were 86 males and 76 females, with a median age 16.0 (5.0-65.2) years). Tumors of the leg represented 88%, those of the femur alone 74%. Primary distant metastases affected 21% of patients. Treatments consisted of surgery (96%), radiotherapy (4%), and/or chemotherapy (97%). Tumor-response to neoadjuvant chemotherapy was good (<10% viable tumor) in 45% of 115 evaluable cases. After a median follow-up of 5.4 years, 5-year overall-/event-free survival expectancies were 75% and 57%, respectively. First events were mainly metastatic. By histology, five-year survival/event-free survival expectancies were 69%/52% for high-grade central and 100%/79% for periosteal osteosarcomas. The absence of primary metastases, no necessity to perform ablative surgery, a good response to preoperative chemotherapy, and achieving a macroscopic surgical remission were prognostically significant upon multivariate testing. Conclusion: Diaphyseal and metaphyseal osteosarcomas share many characteristics. The former may, however, be associated with an increased rate of primary metastases and a lower response-rate to chemotherapy. Overall prognosis and prognostic factors seem comparable. Treatment strategies should follow those established for osteosarcoma.