The genesis and growth of tumors; effects of varying the proportion of protein (casein) in the diet.

Summary There are few reported investigations on the relationship between the proportion of dietary protein, varying within limits that support good body growth and health, and the formation and growth of tumors. This relationship was studied by utilizing diets compounded of commercial foodstuffs and/or semipurified components and ranging in protein content from 9 to 45 per cent. In each experiment, the proportion of dietary protein was varied by substituting casein for cornstarch, all other components of the diet being left unchanged. Four different mouse tumors were studied: Spontaneous mammary carcinomas, skin tumors and sarcomas induced by carcinogenic hydrocarbons, and spontaneous hepatomas of strain C3H mouse. No significant effect on either the incidence or average time of appearance was observed for the spontaneous mammary carcinoma, induced skin tumor, or induced sarcoma. In contrast, the incidence of spontaneous hepatomas was significantly lower in mice fed 9 per cent casein than in those given 18 per cent or higher proportions of casein. The growth rate of spontaneous mammary carcinomas or induced sarcomas was not affected by the proportion of casein fed. In addition, in mice bearing mammary carcinomas, metastases (to the lung) and the duration of life following appearance of the tumors were not influenced by the level of dietary protein. Under the conditions of these investigations, body growth and general health were generally of the same order among the groups of any one experiment. It is emphasized that these studies differ from those in which rations strikingly deficient in quality or quantity are compared with rations adequate for normal body growth. It is concluded that varying the proportion of protein (casein) in the diet, within limits that permit relatively good body growth, probably has little effect on the formation of many types of tumors, but may have a significant effect upon certain special classes. Incidental findings are discussed.