Synergism among oral carcinogens: II. Results of the simultaneous feeding of bladder carcinogens to dogs

Feeding of 0.1 g of 4-nitrobiphenyl per dog, 3 days per week to five purebred female beagle dogs for 26–31 months produced no neoplastic changes in the urinary bladder. Feeding of 2-naphthylamine under the same conditions resulted in the development of a slight to moderate degree of neoplasia of the bladder in four dogs, while the fifth animal was not affected. However, feeding of 0.1 g of 4-nitrobiphenyl together with 0.1 g of 2-naphthylamine 3 days per week to each of five additional animals over the same period of time led to the development of a moderate to extensive degree of neoplasia of the bladder in all animals. These results are interpreted to indicate an additive action of the carcinogens. These studies indicate in addition that 2-naphthylamine is more carcinogenic than 4-nitrobiphenyl.