SOME POSSIBLE EFFECTS OF NURSING ON THE MAMMARY GLAND TUMOR INCIDENCE IN MICE.

A preliminary report on some possible effects of nursing on the mammary gland tumor incidence in mice is presented. 3 litters of mice from an inbred strain of mice with a mammary gland tumor incidence of 88% were fostered by a strain of mice with a tumor indicence of about 10%. Of the 9 females fostered by the low tumor strain 3 developed mammary gland tumors 4 had primary lung tumors and 2 died nontumorus. Among 40 of their progeny who were fostered 12 developed breast tumors 2 had breast and pulmonary cancers 13 had primary lung tumors and 13 died nontumorus. 10 of the 13 progeny of the fostered females which had breast cancer developed similar growths as compared with 4 of the 24 progeny from fostered females which had lung tumors. The respective proportions were 77% and 17%. These results support the belief in the extrachromosomal influence as a cause in the development of mammary tumor.