**Abstract**

Breast/mammary cancer is the most frequent type of cancer and the leading cause of cancer deaths in humans and animals worldwide. The incidence of mammary cancer is continuously increasing worldwide. This increasing trend is attributed partly to the little information on the early changes occurring during mammary gland carcinogenesis. The lack of molecular information on mammary carcinogenesis has impeded the identification of clinically relevant tumor markers beyond histopathology and the introduction of new therapeutic concepts. Numerous factors, molecular and cellular pathways are involved in mammary tumor development and carcinogenesis. To characterize some of the early molecular changes of mammary carcinogenesis, mammary cancer was induced in female rats using the environmental carcinogen 7,12 dimethylbenz (α) anthracene (DMBA) combined with estrogen. Analysis of histopathological alterations in the tissue can observe the process of mammary cancer development. At the molecular level, some genes act as functional components in regulating cancer development, including tumor suppressor genes, oncogenes, and DNA repair genes. In this chapter, the histopathological alterations and the advanced of molecular histopathology stages of breast cancer progression are mainly discussed, including on animal models induced by DMBA-estrogen combination as an effort for cancer prediction and prevention.

**Keywords:** molecular histopathology, protein markers, mammary cancer, carcinogenesis, DMBA
