Breast cancer susceptibility is influenced by the dynamic stromal remodeling of the mammary tissue during its various stages of development. Epidemiological studies suggest that parity reduces a woman’s lifetime risk of developing breast cancer. But this protective effect of pregnancy is neither immediate nor constant, because recent studies show that the developmental window of post-lactational involution significantly increases the risk of parity associated breast cancer. The period of involution is recognized as a sensitive time point when the mammary tissue is highly susceptible to carcinogens. Ethanol is identified as the only dietary factor to increase breast cancer risk in humans. This study tests the effect of ethanol exposure during the developmental window of involution in FVB-MMTV-HER2/neu mice treated with 0, 0.5%, 1% and 2% ethanol mixed in their diets for a period of 14 days. Ethanol does not show an effect on latency, multiplicity or growth rate of primary tumors and metastases to the lungs between the dietary groups. A significant difference is seen in the total tumor burden between the 0 and 0.5% dietary groups. The tumors will be analyzed to study changes in gene expression in order to identify targets in the involution microenvironment that are susceptible to modification by ethanol. Histopathological analysis of brain and liver metastases will be performed in order to establish if this mouse model can be used to study HER2 dependent brain or liver metastases.