Abstract

PIP: Castration of female mice below 6 months of age resulted in a marked reduction of tumor incidence, from between 60-70% in control mice to 9% in castrated mice. Although majority of the tumors appeared during the 1st age period in the controls, they were delayed in the castrated mice to the 2nd age period. Development of neoplasms however cannot be entirely prevented by castration performed at a period between 4-6 months, when the mice have already entered the breeding age. Cancer age is increased in castrated female mice but castration in mice aged 6 months or older does not have any effect on cancer rate or age. Cancer incidence is decreased and cancer age increased when female mice are prevented from breeding, although the effect is not as marked as that of castration. Nonbreeding female mice have a higher cancer age than breeders. Castration is effective in reducing cancer rates because it eliminates the corpora lutea which is responsible for the periodic growth of the mammary gland during pregnancy and in some species, during periods of sexual cycle unaccompanied by pregnancy. Castration allows the mammary gland to remain in an uninterrupted state of rest. The results of this study are the 1st experimental demonstration of internal secretion as an etiological factor in spontaneous cancer development.