The Effect of Pyridoxine on Tumor Growth**

It has recently been observed that the incidence of liver tumors due to p-dimethylaminoazobenzene is much less in rats fed a diet deficient in pyridoxine than in animals on a more complete ration (6). The effect of pyridoxine was evident when the caloric intake of the animals on the two diets was equal, and no similar effect was observed in any of a number of other vitamin deficiencies. Several possible explanations might be offered to account for the suppression of carcinogenesis by the diet low in pyridoxine: (a) the metabolic fate of the azo dye might have been so altered by the deficiency that the effective carcinogenic potency of the compound was reduced; (b) the biochemical reactions by which tumor cells are formed may have been minimized; or (c) tumor cells may have formed as usual, but their subsequent proliferation have been retarded as a result of the dietary deficiency. Accordingly a study was made of the response of a number of different types of tumors to synthetic diets low in pyridoxine. The neoplasms included developing mouse tumors due to the injection or local application of methylcholanthrene, preformed primary mouse tumors, and three types of transplantable tumors. Since the most successful results were obtained with the latter types, the appropriate experiments are described in detail.