Breast cancer and hormone receptor positive (HR+) breast cancer incidence vary across the world with higher incidence in developed countries. Most risk factors for breast cancer are environmental and involve increased exposure to estrogen. However, known risk factors of breast cancer explain approximately 50% of breast cancer risk; thus other risk factors that are environmental, estrogenic and/or related to development might be responsible for the remnant risk. Xenoestrogens are such chemicals with wide presence in developed countries and urban areas which have been shown to increase risk of breast cancer in in vitro and animal studies. Human studies looking at the association of xenoestrogens with breast cancer have been equivocal. One of the reasons for this has been an absence of unexposed populations in developed countries. We hypothesized that urban incidence rates of breast cancer and HR+ breast cancer will be higher than rural rates and set out to investigate this hypothesis by comparing the two populations. As a part of this dissertation using a series of studies which utilized data from the Gharbiah Population-based Cancer Registry (GPCR) in Egypt, we showed that urban incidence of breast cancer was three to four times higher than rural incidence. This trend held true over an eight year period for all age-groups and districts. We also showed that HR+ breast cancer incidence was two to three times higher in urban areas compared to rural areas. Further investigation into other female malignancies showed six times higher incidence of uterine cancer in urban areas than rural areas. Since both breast and uterus are organs susceptible to estrogenic effects, a higher urban incidence of these malignancies suggested a higher exposure of urban women to estrogenic risk factors. In the absence of significant differences between urban and rural women with regards to reproductive factors, healthcare access and health behavior, differences in exposure to environmental sources of estrogens emerges as a probable factor for higher urban incidence of breast and uterine cancer. Future studies are needed to investigate individual level differences in exposure to environmental sources of estrogen such as xenoestrogens, considering the presence of appropriate comparison populations