Tumor Incidence in Reciprocal F 1 Hybrid Mice — A x D High Tumor Stocks

With the increase in the number of inbred stocks of mice interesting and important data may be obtained in the study of the incidence of certain types of cancer by making reciprocal crosses. Previously all reports on the development of tumors in hybrid generations have been observations secured by crossing strains of animals which differ greatly in the percentage of animals showing growths. In this paper we wish to consider the spontaneous tumor incidence in mice of the first filial generation made by mating individuals of two strains in which mammary gland tumors frequently develop.

Stocks of Mice. (1) The “D” Strain. A sub-strain of the Little dilute brown race, previously described by Murray⁹ was used as one parental race. (2) The “A” Strain. The other stock of animals employed was originally descended from the Bagg albino strain. Data on the tumor incidence has been reported by Strong¹³ and Bittner. 1 A report comparing the breeding behavior and tumor incidence of the D and the A stocks is in press (Bittner and Murray). 2

Females from each strain were used in breeding the first generation hybrids. When the A stock females were mated to D males, the hybrids were termed ADF₁; when the D females were crossed to A males the resulting generation mice were called DAF₁. All the F₁ individuals were employed as breeders in transplantation studies.

The number of animals dying non-cancerous or developing tumors are grouped in monthly age periods in Table I. The proportion of the total cancerous mice recorded in bimonthly periods is represented graphically in Fig. 1.