Effects of molybdenum and tungsten on mammary carcinogenesis in SD rats

Virgin female rats of the SD strain were fed ad libitum a nutritionally adequate semipurified diet and demineralized water (groups 1 and 2), or the same diet with 10 ppm molybdenum (group 3) or 150 ppm tungsten (group 4) added to the drinking water. The animals in groups 2-4 received a single iv injection of 5 mg N-nitroso-N-methylurea (NMU; CAS: 684-93-5)/100 g body weight at 50 days of age. One hundred and twenty-five days after the NMU treatment, group 2 exhibited a 50.0% incidence of mammary carcinoma. Group 4 exhibited a significant increase in carcinoma incidence (79.2%) and the value for group 3 (45.5%) was not significantly different from that of group 2. The carcinoma incidence of group 3 (50.0%) was significantly lower than that of group 2 (90.5%) or group 4 (95.7%) 198 days after NMU treatment.