7, 12- Dimethylbenz-(a)-anthracene (DMBA) has been used for a long time to induce rat mammary gland carcinogenesis. In a previous paper we described the effects of diet, of non-steroidal anti-inflammatory drugs and the combination of these two factors on breast cancer. We also pointed out that DMBA tumor generating process is still poorly understood. The present study attempts to explore whether P53 or the pro-apoptotic protein Bcl-2 are potential targets of DMBA in its induction of breast tumors in the Sprague-Dawley rat breast tumorigenesis model. Our results indicate that the DBMA-induced tumors are apparently the result of P53 inactivation. This inactivation results in tumorigenesis, probably aided by the absence of Bcl-2 in the tumor cells of the Sprague-Dawley rat animal model. We discuss the potential mechanisms by which P53 inactivation results in tumorigenesis.