Cancer of the Cervix of the Uterus in Hybrid Mice Following Long-Continued Administration of Estrogen

Abstract

2 strains of mice (one is C57 which is definitely resistant to mammary cancer but has poor tolerance for estrogenic treatment and the other was CBA which has an incidence of 70% of spontaneous tumors in force bred animals but tolerates estrogen treatment well) were hybridized in the hope that the F1 generation would tolerate estrogenic treatment well and to determine the incidence of hypophysial and mammary tumors. The resulting offsprings were grouped into 2: CC1 consisting of 24 females and CC2 consisting of 20 females; both groups received estrogenic treatment for more than 1 year. Majority of the animals received 16.6 mg/week estradiol benzoate and some received as much as 50 mg/week starting at 28-56 days of age and maintained at the same level throughout the animals lives. Similar number of untreated hybrid mice served as controls. Lesions and cervical carcinomas appeared in 15 of the 24 mice (62%) and 10 of 20 (50%) mice which survived the treatment for more than 1 year. The lower incidence of cervical lesions in the CC2 group was probably due to the 60% incidence of mammary tumors which occurred at an earlier age than the cervical lesions. Genetic factors involved in mammary cancer had little effect in the carcinogenesis of the cervix uteri. No cervical lesions appeared in either group before 400 days of age and none appeared in the CC1 group before 450 days of age. It is concluded that with this hybrid stock chronic estrogenic stimulation at this level usually requires longer than 400 days for the appearance of cervical lesions and that estrogen is a very important factor in cervical carcinogenesis.