Finally, the large proportion of patients clinically diagnosed with breast cancer in whom no mutations were found, especially among those with complete sequence of the BRCA1 and BRCA2 genes, supports the fact that the development of breast and ovarian cancer not only depends on a reduced spectrum of genetic factors associated with mutations in these particular genes, and that other genetic and non-genetic factors must be considered. The gene discussed is BRCA1; the disease is breast cancer.