The proposed study is designed to help understand the occurrence of breast cancer in very young women. About 5% of all breast cancers occur before the age of 35 years. Unfortunately we do not have means of prevention or early detection of breast cancer for this age group, as the dense breasts do not allow the use of most detection modalities. It is therefore of utmost importance to understand the genetic background of these women as well as the genetic characteristics of their tumors in order to develop proper control measures.  This study will investigate particularly events in genes that are known to be associated with the occurrence of breast cancer and other tumors, such as P53; but which are not routinely tested for. The team will study the role of these genes in breast cancer patients of Jewish and Arab origin, participants of a large population based study that collects big amounts of background information about the participant and her family and collects DNA and tissue samples to allow for studying possible etiologies and characteristics of this tumor type.