BONE SARCOMA CHARACTERISTICS AND DISTRIBUTION IN BEAGLES INJECTED WITH RA-226

A total of 155 primary bone sarcomas were found in 131 of the 246 beag les injected with Ra-226 and 5 primary bone sarcomas were found in 4 o f the 158 unexposed controls. Of these 155 bone sarcomas, 146 (94%) we re osteosarcomas and 9 were non-osteosarcomas. An additional 31 primar y bone sarcomas (28 osteosarcomas) developed in 44 dogs terminated fro m the main study because of limb amputation for bone sarcoma. Non-oste osarcomas predominated in both the controls and the second lowest of s ix logarithmically increasing dose levels (there were no bone sarcomas in the lowest dose group). Osteosarcomas predominated at the higher d ose levels, and incidence tended to increase as dose increased. The 14 6 osteosarcomas were distributed quite evenly between males and female s (72:74). Of the 9 non-osteosarcomas, 6 occurred in males and 3 in fe males. The ratio of bone sarcomas of the appendicular skeleton to thos e in the axial skeleton was 110:45, with osteosarcomas occurring more often in the appendicular skeleton (108:38). Cases of multiple primary bone sarcomas in dogs injected with Ra-226 were found only in the fou r highest dose groups. Amputations were performed on 44 of the 96 dogs (94 injected and 2 unexposed) that developed appendicular bone sarcom as. A statistical study of the distribution of bone sarcomas among 16 separate bone groups showed a statistically significant correlation to cancellous skeletal surface, but the variability among bone groups wa s too large for this relationship to be of real predictive value. It i s postulated that the distribution of bone sarcomas reflects primarily the relative cell division rates in the bone groups and secondarily t he radiation dose distribution, with the highest occurrence of bone sa rcoma in the humeri, pelvis, femora and tibiae/fibular tarsal, and no occurrence in the coccygeal vertebrae, sternum, forepaws or hindpaws.