This experimental study was designed to evaluate the efficacy of associated naturally occuring antioxidants in the prevention of chemically induced breast cancer using DMBA in virgin female Wistar rats. Rats were randomly allocated to three groups: control group (CG; n = 20), induction group (IG; n = 100), and prevention group (PG; n = 70). A single dose (65 mg/kg) of DMBA was administered in the IG and PG animals at 50 days of age. PG animals also received a single dose of alpha-tocopherol (200 mg/rat) 1 hour after DMBA administration and an association of selenium (p-XSC, 40 ppm/day/rat) and ascorbic acid (540 mg/day/rat) in drinking water, daily, from carcinogenic induction until necropsy. Macroscopic study and pathology revealed a significantly lower development of neoplasms in the PG animals (p < 0.05); the number of rats with mammary tumors, breast cancer incidence, and the number of malignant breast tumors per rat as well as per tumor-bearing rat were significantly decreased in the PG animals. Other types of primary neoplasms existing in the IG animals totally disappeared in the PG animals. Immunostaining to hormone steroid receptors (ER and PR) and cathepsin D was similar in both groups. Overexpression of p53 and metallothioneine was significantly increased in the PG animals (p < 0.05) and immunostaining to bromodeoxiuridin and Ki-67 was also stronger in the remaining tumors in the PG animals. These data thus add to the accumulating evidence that those micronutrients in combination seem to be effective in reducing the incidence of malignant tumors. Nevertheless, remaining tumors seem to present more aggressive behavior and characteristics of drug resistance.