Further Studies on the Relation of Functional Activity to Mammary Carcinoma in Mice
The American Journal of Cancer
In previous studies the writer has noted that the rapid breeding of female mice, coupled with the prevention of nursing, increased the incidence of spontaneous mammary carcinoma (1, 2, 3). It was concluded that ovarian stimulation of the mammary gland and possibly the chemical irritation of retained glandular secretions were factors associated with the formation of the mammary tumors. At the time this earlier work was done there were no strains of mice available for experimental study which had
... been inbred for a considerable time and had been selected for " low-tumor " incidence. Three years ago the writer obtained from Dr. C. C. Little's laboratory at Bar Harbor mice in which the genetic variables had been reduced to a minimum as a result of inbreeding. The incidence of spontaneous tumors had been noted over several years. The purpose of this paper is to report the results of experiments designed to test the relation of functional activity of the mammary gland to the incidence of spontaneous carcinoma in this organ as shown in these carefully selected strains of mice. A " functional test" will also be described which has been used to distinguish those individuals whose constitution is favorable to the growth of mammary carcinoma from those apparently constitutionally unfavorable to the growth of such tumors. The relation of functional activity to what Murray and Little (4, 5, 6 ) have described as " extrachromosomal influence " in relation to mammary gland carcinoma will also be considered. The following results are preliminary and will be presented more fully at a later date, on the completion of the work, STRAINS OF MICE USED ( 1 ) Strain CBA: This was a strain of low-tumor mice (now called strain " X ") obtained from the Jackson Memorial Laboratory in 1933. The mice were of a wild-type color, inbred since 1921. Up to 1933 their record shows " no tumors of any description in individuals whose average age of life for the past ten generations is twenty-one months." ( 2 ) Strain C57: This is a low-tumor strain obtained from Jackson Memorial Laboratory in 1933, at which time its history showed no recorded instance of carcinoma of the breast during the past ten years. The mice are black and have been inbred for ten years.