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The Incidence of Diethylstilbestrol-induced Cancer in Reciprocal F₁ Hybrids Obtained from Crosses Between Rats of Inbred Lines That are Susceptible and Resistant to the Induction of Mammary Cancer by This Agent

( Division of Research and Industry, University of Miami, Coral Gables, Fla.)

1. Diethylstilbestrol-induced mammary adenocarcinoma occurred in an average of 632 days in eighteen (24 per cent) of 76 hybrid progeny obtained from crosses between resistant strain male and susceptible strain female rats.

2. Among 56 similarly treated hybrids from reciprocal crosses, twelve (21 per cent) developed mammary adenocarcinomas in an average of 551 days.

3. Induced adrenal tumors were observed in twelve of the hybrids from resistant strain females and in six of the hybrids from the reciprocal crosses. Adrenal tumors were more frequent in the males than in the females of both groups of hybrids and the susceptible parental strain.

4. Diethylstilbestrol-induced bladder calculi and cancer occurred in both parental strains and in both groups of hybrids but were most frequent in the male progeny of Copenhagen line 2331 females.

5. Spontaneous neoplasms, probably unrelated to the treatment, occurred with equal frequency in both hybrid groups.

6. The F₁ hybrid progeny from reciprocal crosses between diethylstilbestrol-resistant and diethylstilbestrol-susceptible rats showed an equal susceptibility to tumors induced by this agent.

Received 4/ 9/52.