Osteosarcoma of the Diaphysis: A Report from the Cooperative Osteosarcoma Study Group (COSS)

The diaphyses of long tubular bones are a very rare primary site of osteosarcomas and their characteristics and disease course are only poorly defined.

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.

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.

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.