Causes of mortality in chickens that regressed a Rous sarcoma virus-induced tumor

Rous sarcomas were induced in 6-week-old chickens of several genetically different stocks: inbred lines C, 6(1), 6(3), and 7(2); crosses of inbred lines (6(3) X 7(2)) F4 and (6(1) X 15(1)) F2 X 6(1); and reciprocal crosses (15(1) X 100) F1 X 15(1) and (15(1) X 100) F1 X 100. The resulting tumors were scored for size six times during a 10-week period. Females that had completely regressed their sarcomas were placed in individual laying cages and examined weekly for reappearance of a tumor. After death, the probable cause was determined by necropsy. The major causes of death in the pooled sample of 49 females were fatty liver hemorrhagic syndrome (24.6%), reproductive disorder (14.2%), Marek's disease (12.2%), and lymphoid leukosis (6.1%). Elapsed time between tumor regression and death from any cause ranged from 21 days to 1930 days (5.3 years). One tumor recurred, this in a bird which eventually died with a massive sarcoma in the left wingweb and Rous metastasis in liver tissue. These data provide evidence of specific resistance to neoplastic disease.