Exposure to genotoxic stresses such as cosmic radiation and second-hand tobacco smoke may increase the risk of breast cancer formation. Towards an understanding of how exposure to these genotoxic agents affect breast cancer biogenesis, we have shown that treating non-tumorigenic immortalized breast MCF 10A cells with low doses (0.1 Gray) of radiation as well as cigarette smoke condensate can generate a neoplastic breast cancer phenotype. The transformed phenotype promoted increased mammosphere numbers, altered cell cycle phases, and increased invasion and motility. In addition, exclusion of Hoechst 33342 dye, a surrogate marker for increased ABC transporters, was observed, which indicates a possible increase in drug resistance. Furthermore, differential gene expression profiles were generated from the individual and combination treatment. Overall, the results indicate that when normal breast cells are exposed to low dose radiation in combination with cigarette smoke condensate a phenotype is generated that exhibits traits indicative of neoplastic transformation. Taken together, these results provide a new insight into a possible etiology for breast cancer formation in individuals exposed to cosmic radiation and second-hand smoke.