Slight promotion effects of intermittent administration of testosterone propionate and/or diethylstilbestrol on 3,2′-dimethyl-4-aminobiphenyl-initiated rat prostate carcinogenesis

In order to determine the effects of intermittent hormonal manipulation on the promotion stage of rat prostate carcinogenesis, testosterone and/or estrogen were administered to F344 rats for 40 weeks after 20-weeks treatment with the prostate carcinogen, 3,2′-dimethyl-4-aminobiphenyl. For this purpose testosterone propionate (TP) and diethylstilbestrol (DES) were introduced into silastic tubes, 2- and 0.5-cm long, respectively, and implanted into the subcutis for seven repeated cycles of 30 days treatment and 10 days withdrawal. Intermittent administration of TP resulted in suppression of ventral prostate adenocarcinoma development and slight but non-significant increases in the incidences of invasive carcinomas of the lateral prostate and seminal vesicles. Intermittent administration of DES completely suppressed tumorigenesis in all sites and the combination of TP and DES generally inhibited prostate tumor development. Thus, under the present experimental conditions, no strong enhancing effects of cyclic hormonal manipulation were observed on rat prostate carcinogenesis. Indeed, the opposite appeared to be the case.