Cnapter 9 



THE MILK INFLUENCE IN TUMOR FORMATION 



^A* John J. Bittxer, Roscoe B. Jackson Memorial Laboratory. 



New approaches to the problem of breast cancer etiology in mice devel- 

 oped following the advancement of the extra-chromosomal theory. Inde- 

 pendent work was published almost simultaneously by the Staff of the 

 Jackson Memorial Laboratory (28) and Korteweg (20) using strains which 

 had been sent from the Jackson Laboratory. This work has been confirmed 

 in several other experiments with different strains of mice (25-27. 29, 21-23, 

 19, 5. 8-9. 17-18). 



In these experiments reciprocal matings were made between high and low 

 breast tumor strains of inbred mice. When the maternal parents were 

 members of the high tumor strains it was observed that the Fi and Fo 

 generation hybrids had a higher breast tumor ratio than if the paternal 

 parents were representatives of the high tumor line. This maternal 

 influence has three possible explanations: 



A. That some influence is transmitted in the milk of the potentially 

 breast cancerous females to their young while nursing. 



B. That some influence is transferred to the progeny of breast cancerous 

 mothers during uterine development. 



C. Cytoplasmic inheritance. 



To date all the experimental evidence emphasizes the role played by 

 the milk influence. In all. at least three "influences" must be taken into 

 consideration in the development of breast cancer, at least in mice. These 

 are: 



1. A "breast cancerous producing influence" present in the milk of 

 cancer stock mothers. 



2. A breast cancer susceptibility due to one or more dominant factors 

 transmitted by breast cancer strain mice. 



3. An ovarian or hormonal influence which may or may not be asso- 

 ciated with breeding, depending upon the strain of mice studied. 



The evidence supporting this explanation follows. 

 To test the eft'ects of foster nursing on the breast tumor incidence, young 

 born to high breast tumor females were removed soon after birth and were 



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