Breast cancer is the most common cancer affecting women in the United States. There are at least two major genes (BRCA1 and BRCA2) that, when mutated, can cause breast cancer. These genes can be passed from parent to child, increasing the risk of developing cancer in children whose parent carries these genes. The BRCA1 and BRCA2 genes are located on chromosome 17 and chromosome 13 respectively. There is a 90% chance of developing breast cancer for a woman carrying these mutated genes. In contrast, men with the BRCA1 gene are at no risk of developing breast cancer, but those with the BRCA2 gene are at high risk. It is important to note that mutations in these genes can be passed on to children from either parent. A man with a mutation is just as likely to pass this gene on to his children as a woman with a mutation. Hereditary cancer occurs at a young age. For example, a woman in her 20s with breast cancer is more likely to have a hereditary type of cancer than a woman in her 50s. (http:www.familycancer.org/FamHist.stm)BRCA1 and BRCA2 are tumor suppressor genes, these genes also called "anti-oncogenes" which are normally involved in the regulation of cell growth, the proteins inhibit cell proliferation , which is crucial for normal cell development and differentiation. (Britanica online). Since the discovery of BRCA1 and BRCA2 in 1994 and 1995, approximately 80% of women who inherit mutated forms of these genes will develop breast cancer during their lifetime, usually at a relatively early age, and women with BRCA1 mutations will have a high risk of developing ovarian cancer as well. Kudson proposed a two-mutation theory of cancer causation in 1971. His theory stated that all cancers are of two kinds, hereditary and sporadic. In the case of...... middle of article ....... Hereditary breast cancer. European Journal of Cancer Care. 5, 13-203.-Social and ethical issues related to genetic testing for breast cancer. Obtain at http://www.ncgr.org/gpi/odyssey/BCAN2/gtest.html 10/29/984.-Kinzler, Kenneth W. and Vogelstein, Bert. 1997. Breast cancer susceptibility genes BRCA1 and BRCA2. Nature. V. 386. 761-763.5.-Marx, Jean. 1997. Possible function found for breast cancer genes. Science vol.276. 531-532.6.-McCain, L. and Dilligham, C., 1997. Genetic mutation associated with breast cancer. Get from http://www.ncgr.org/gpi/odyssey/BCAN2/genrisk.html 10/12/987.-Tumor suppressor gene" Get from http://www.eb.com:180 > 10/19/98, search word: tumor suppressor gene.8.-Risk of breast and/or ovarian cancer in Jewish women: role of 185delAG and other mutations in the BRCA1 and BRCA2 genes http://www.givf.com/brca1.html. 10/12/98.