Occurrence of metastases in beagles with skeletal malignancies induced by internal irradiation

Metastases from malignant bone tumors often are responsible for the fatal effects of these cancers. Characteristics of primary skeletal malignancies in beagles injected with bone-seeking radionuclides were studied by Thurman (1971) and summarized by Thurman et al. (1971). There were 212 tumors in 186 of these dogs for which we subsequently received information on bone tumor metastases. Evaluation of bone and soft tissue slides from these animals allowed us to compare parameters reported previously with the occurrence of grossly apparent bone tumor metastases. Data included growth-rate of the primary tumor, volume of the primary tumor at death, sex of the animal, growth period of the primary tumor, degree of calcification of the primary tumor, skeletal location of the primary tumor, cumulative radiation dose to the skeleton, dose equivalent to the skeleton, and year of death. For most of the comparisons, no significant differences could be established between dogs with and without metastases. However, tumor volume at death appeared to be correlated with probability of metastasis (p < 0.05), with the larger tumors being associated with higher rates of metastasis. Comparisons of dogs with and without metastases as a function of tumor growth-rate did not, for the most part, yield significantly different results between groups. Exceptions were when only one tumor per dog was considered for animals with multiple primary tumors and when only the tumor with the longest doubling time was included for all dogs with multiple primary tumors (p < 0.02). This effect was a result of only two tumors with doubling times > 45 d. Both had been characterized by Thurman (1971) as among the tumors with the least uncertainty in calculated doubling times. Rates of metastasis in dogs with primary tumors in paired bones were significantly higher than corresponding values of dogs with primary tumors in unpaired bones. Metastases in dogs with primary tumors in the ribs appeared to be more pronounced and those in the thoracic vertebrae appeared to be less pronounced than for animals with primary tumors in other bones as compared with the average for the whole skeleton.