The functional activity of the breast in relation to mammary carcinoma in mice.

The following experiments were designed to test the possible relation of functional disturbances of the breast to the incidence of mammary carcinoma in mice.

A carefully inbred strain of animals with a well-known low rate of tumor incidence was selected. Mammary tumors in females from this strain that are allowed to breed normally do not appear until the animals are between one and a half to two years of age. The females were large, vigorous, prolific individuals, and suckled their young successfully.

Females from the above strain were divided into two groups, one serving as a control was allowed to breed normally, i. e., the females were remated only after nursing their litters for about six weeks. The test animals from the same family were then bred under the following procedures designed to subject the mammary tissues to abnormal conditions:

1. Females bred when very young (two to three months old), and their litters removed immediately after parturition, or not more than twelve hours later, and the mothers remated at the œstrus that promptly follow parturition.

2. Females bred when six to nine months old, and treated as in the above group.

3. Various combinations of alternating periods of suckling of one litter and non-suckling of the next litter, etc.

4. Ligating mammary ducts to the nipples on one side of the body when the females were about half way through the period of pregnancy, followed by suckling of litter and remating after weaning. The operative ltrauma was minimized as much as possible. No attempt was made to prevent suckling on the unoperated side of the body.

The results are based on the records of fifteen females with spontaneous tumors, all of which have been found to be mammary carcinoma on histological study.