Genetic Evaluation Influences Treatment Genetic breast cancer accounts for about 10 percent of all breast cancer cases. Of the known hereditary mutations that have been shown to cause breast cancer, BRCA (BReast CAncer) accounts for over 90 percent. There are two BRCA genes: BRCA 1 (located on chromosome 17) and BRCA 2 (located on chromosome 13). For patients who are BRCA-positive, there are a variety of treatment and preventative measures that can be used against breast cancer. Initially, increased breast imaging allows physicians to keep a close eye on any suspicious lumps or masses. It may be beneficial for the patient to receive digital mammography as well as breast MRI, alternating the imagings every six months. Tamoxifen may also be prescribed for some BRCA 2-positive patients as 80 percent of these breast cancers will be estrogen receptor-positive. It has become increasingly popular for patients which are BRCA-positive to opt for bilateral mastectomies or salpingo-oopherectomies (BSO). These procedures can almost completely eliminate the risks of developing breast or ovarian cancer (90 percent with mastectomy and 96 percent with BSO). Adding to this trend is the significant advances that breast reconstruction has undergone in the last several years.