[Effect of molybdenum and tungsten on mammary carcinogenesis in Sprague-Dawley (SD) rats]

Virgin female rats of SD strain were given ad libitum a nutritionally adequate semipurified diet containing 0.026 ppm molybdenum and deionized water (groups 1-3) or the same diet with 150 ppm tungsten and the drinking water (group 4). Group 1 was used as control. After 15 days, all the animals in groups 2-4 received an intravenous injection of N-nitroso-N-methylurea (NMU) 5 mg/100 g body weight. One week after administration of carcinogen, 10 ppm Mo was added to the drinking water in group 3. After 125 days, the mammary cancer incidence in group 4 (79.2%) was significantly higher than that in group 2 (50.0%) or group 3 (45.5%) (P less than 0.05). After 198 days, the average number of mammary cancer in each animal and mammary cancer incidence in group 3 (1.5 and 50.0%) were obviously lower than those in group 2 (2.0 and 90.5%) or group 4 (2.6 and 95.7%). The first palpable mammary tumor was found in the W-supplemented group only 56 days after the injection of NMU, whereas in the W-unsupplemented and Mo-supplemented groups, the first mammary tumor was observed 71 and 85 days after NMU treatment. Of these 181 mammary tumors, 177 (97.8%) were adenocarcinoma or papillary carcinoma, only 4 (2.2%) fibroadenocarcinoma. The results of this study show, for the first time, the inhibitory effect of Mo on the mammary carcinogenesis and promoting effect of Tungsten, an antagonist of molybdenum, on the tumor growth.