Continuous Versus Cyclic Estrogen Administration: Mammary Carcinoma in C3H Mice

Summary

Mammary carcinoma incidence in male or castrated male C3H mice was lower when diethylstilbestrol (DES) was given in the diet in intermittent cycles of 2, 7, 14, or 28 days than when given on a continuous basis. Generally the latent period of tumor formation was shortened by treatments which produced high tumor incidence. Continuous treatment with DES also significantly reduced testis, seminal vesicle, and body weights (but not pituitary weight) when compared with cyclic treatment with DES in which equivalent doses were used. Castrated males had significantly higher tumor incidence and shorter latent period than did intact males. Of the cyclic regimens, the shortest (2 days) produced the highest tumor incidence in intact males, whereas it produced the lowest tumor incidence in castrated males.