Small-cell osteosarcoma: correlation of in vitro and clinical radiation response.

Small-cell osteosarcoma is an entity which shares some clinical and pathological features with both classic osteosarcoma and Ewing's sarcoma of bone. While noted to be "not radiosensitive" when first described, a retrospective review the National Cancer Institute experience of five patients with small-cell osteosarcoma treated with radiation therapy following biopsy (three pts) or limited excision (two pts) showed local control in all five patients with two long-term disease-free survivors (12, 18 years). This compares to three patients treated with surgery alone where one patient failed locally and one patient is a long-term disease-free survivor (7 years). We have studied the in vitro radiation response of a recently established small-cell osteosarcoma cell line (TC-252) and compared its response with that of a classic osteosarcoma cell line (U2-OS) and an Ewing's sarcoma cell line (5838). The small-cell osteosarcoma line responded with a similar Do and extent of PLDR compared to the Ewing's line and was different from the in vitro radiation response of classic osteosarcoma. Based on this small clinical series and the in vitro radiation studies, we conclude that small-cell osteosarcoma is a radioresponsive tumor. Definitive radiation therapy or conservative surgery plus radiation therapy are effective alternative therapeutic options, compared to ablative surgery, for the local treatment of this uncommon bone tumor of children and young adults.