BONE SARCOMA CHARACTERISTICS AND DISTRIBUTION IN BEAGLES FED SR-90

A total of 66 primary bone sarcomas were diagnosed in 47 beagles; 43 of these dogs were part of the 403 beagles fed 90Sr and 4 were part of the 162 controls. Multiple primary bone sarcomas were found in 15 of the 47 beagles (32%). The incidence of multiple primary bone sarcoma was restricted to the two highest dose groups, except for a single control dog which developed two bone sarcomas. A threshold-like radiation dose response was observed; no sarcomas were observed in the lowest three dose groups, but the number of primary bone sarcomas increased rapidly in the higher dose groups. Of the 66 primary sarcomas, 49 were osteosarcomas (74%). As the dose increased, the proportion of osteosarcomas increased sharply, 4/10 (40%), 26/29 (90%), and 16/18 (89%), in the three highest dose groups. Thirteen of the bone sarcomas of other types occurred in males, and 4 in females, whereas 21 osteosarcomas occurred in males, and 28 in females. The ratio of bone sarcomas of the appendicular skeleton to those in the axial skeleton was 40:26, with osteosarcomas occurring more often in the appendicular than the axial skeleton (32:17), whereas nonosteogenic tumors showed no predilection (8:9). A statistical study of the distribution of bone sarcomas among 16 separate bone groups showed a correlation only with the distribution of cancellous bone volume-to-surface ratio and not with either skeletal mass distribution or dose distribution. The highest occurrence of sarcomas was in the humeri, femora, and mandible, and no occurrence in the coccygeal vertebrae, paws, or sternum. It is postulated that the distribution of bone sarcomas reflects a critical combination of the osteosarcoma precursor cell population, their cell division rate, and the radiation dose absorbed by these cells.