The association between breast cancer initiation and prolonged exposure to estrogen suggests that this hormone may also have an etiologic role in such a process. On the other hand, many studies have found an association between human cancer and exposure to agricultural pesticides such as parathion, an organophosphorous pesticide used in agriculture to control mosquito plagues. However, the key factors behind the initiation of breast cancer remain to be elucidated. The aim of this study was to determine the effect of 17beta estradiol (estrogen) and parathion on protein expression in cell transformation of human breast epithelial cells in vitro. Estrogen and parathion alone and in combination induced malignant transformation of an immortalized human breast epithelial cell line, MCF-I0F, as indicated by anchorage independency and invasive capabilities. The results indicate that a combination of estrogen and parathion increased the expression of related cell adhesion proteins such as Dvl, Notch, CD146 and beta catenin. In conclusion, it can be suggested that pesticides affect human breast cell adhesion changes indicative of transformation.