Mammary Tumors and Mammary-Gland Development in Hybrid Mice Treated With Diethylstilbestrol for Varying Periods

Abstract

Male and female mice, F₁ hybrids of strains C3H and RIII, were implanted with diethylstilbestrol pellets for varying periods. The mammary-tumor incidence was high in untreated as well as in estrogen-treated virgin females of reciprocal crosses. Normal C3H × RIII females developed mammary tumors at an early age; tumors appeared sooner when the mice were exposed to a pellet of diethylstilbestrol for 8 weeks, but prolonged treatment did not further reduce the mean tumor age. Normal RIII × C3H females developed tumors much later than the reciprocal cross; the mean tumor age was greatly reduced by exposure to a pellet for 8 weeks and still further reduced by treatment for life. C3H × RIII males exposed to a pellet for 6 or 8 weeks had a much higher incidence of tumors and a lower mean tumor age than RIII × C3H males with similar treatment. With prolonged diethylstilbestrol treatment both hybrids had a high incidence of tumors; the tumors developed slightly earlier in C3H × RIII males. The differences in incidence of mammary tumors and in mean tumor age between the two hybrid groups suggest that the agent in the milk of strain C3H is more active than that of RIII. Whole mounts of mammary glands of mice treated with diethylstilbestrol showed dilated ducts, clusters of distended acini, and a characteristic lack of uniformity in different areas. Within 4 to 6 weeks after removal of the pellets, the glands of females resembled those of normal mice; the ducts of male glands became narrow and the acini regressed almost completely except for those organized into nodules.