Breast cancer research still in its infancy in Sudan, although, the disease is the most common type of cancer and the leading cause of cancer death among Sudanese women. The life time exposure to estrogen for long periods is highly implicated with the risk of developing the disease, this steroid hormone exerts its effect through the action of its nuclear receptor (ERa) which is encoded by ESR1 gene. This book is an attempt to shed a light on the problem of breast cancer in Sudan, and the genetics behind the association between the exposure to estrogen hormone and the risk of breast cancer, and different clinical and histological characteristics of breast cancer. Furthermore, it also addresses the potential role of different genetic variants of ESR1 gene on the status of estrogen receptor.