Growth of Sinclair swine melanoma as a function of age, histopathological staging, and gonadal status

We have analyzed the association between host hormonal status and growth rate of congenital exophytic melanomas of Sinclair swine. The growth of multiple exophytic lesions during the first year of life of intact males, orchiectomized males, intact females, and ovariectomized females was quantitated using a proliferative index which assigned a numerical value to fixed increments of gains or losses in tumor volume. The proliferative index from 6 wk (gonadectomy at 6 wk) to 52 wk of age of each treatment group was statistically increased from 0 (P less than 0.01) except that of gonadectomized females. The proliferative indices from lesions in gonadectomized females were significantly lower than those from intact males, intact females, and gonadectomized males. A total of 93 exophytic tumors from 63 swine were biopsied and histopathologically staged according to the degree of progression or regression and analyzed as a function of animal age. There were no Stage I and only two Stage II lesions at the time biopsies were taken. Twenty-six of 32 (81.2%) Stage III tumors were found in swine of both sexes less than 26 wk of age of which 71.8% were found less than 10 wk of age, while 20 of 29 (68.9%) were Stage IV, and only 3 of 32 (9%) were Stage V lesions present in this age group (P less than 0.001, chi 2). Only 20.7% of Stage IV tumors were present prior to 6 wk of age. Preliminary results suggest that castration of either sex also altered tumor histopathology. Our data suggest that a reduction in gonadal steroid secretion was associated with a decrease in exophytic tumor growth rate and regression in animals of both sexes during the first year of life in Sinclair swine. The effect in female swine was due to significant reduction in the proliferative index over the first 6 mo of age.