 About half of hereditary breast–ovarian cancer syndromes involve unknown genes.Furthermore, certain latent viruses, may decrease the expression of the "BRCA1" gene and increase the risk of breast tumors.GATA-3 directly controls the expression of estrogen receptor (ER) and other genes associated with epithelial differentiation, and the loss of GATA-3 leads to loss of differentiation and poor prognosis due to cancer cell invasion and metastasis.