Growth of mammary tumors in a high and a low mammary tumor strains of mice established from the same basal stock of Swiss albino.

The growth of spontaneous mammary tumors and of tumors transplanted into the animals with different hormonal conditions was compared between SHN and SLN strains of female mice established from the same basal stock of Swiss albino as a high and a low mammary tumor strains, respectively. There were little differences between strains in the growth of spontaneous mammary tumors of multiparous mice which appeared first. The growth of transplanted mammary tumors was not affected by the hormonal conditions of the hosts in either strains. However, the tumors became palpable one week after transplantation in SHN, which was 2 weeks earlier than in SLN. These findings indicate that the selection of animals for mammary tumorigenesis is effective on the time and frequency of malignant transformation of mammary cells and on the ""take'' of transplanted tumor cells, but not on the growth potentiality of already established tumors. They further suggest autonomy in the growth of mammary tumors in both strains of mice.