Mammary cancer developed with the same incidence and at the same average cancer age in 22–24-day-old test animals following the injection of 5 × 10-2, 10-3, or 10-4 gram-equivalents of a transplanted mammary carcinoma containing the mammary tumor agent (MTA).

Lower incidences were observed in Zb, Ax, and F1 mice injected at 133–154 days of age, yet the highest incidence was recorded in adult litter-mate ZBC mice which obtained the extract diluted 10,000-fold, and the differences were of statistical significance.

In most groups, infection of the mothers and incidences and cancer ages seen in the progeny could not be correlated with the concentration of the agent in the extracts.

The development of mammary cancer in the progeny of experimental females was influenced by the genetic constitution of the offspring but was not dependent upon the relationship of the mice to the original source of the MTA.


Assisted by grants from the National Cancer Institute of the National Institutes of Health, U.S. Public Health Service, the American Cancer Society upon recommendation of the Committee on Growth of the National Research Council, the Minnesota Division of the American Cancer Society, and the Graduate School Cancer Research Fund of the University of Minnesota.

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