breast cancer is an important cause of morbidity and mortality in women .Genetics of female contributes to her risk of having breast cancer . this disease is still discovered in their late stages due to the negligence of females inspite of self inspection and clinical examination of the breast .the identification of markers that could predict the tumor behavior is important in breast cancer management , staging, evaluation of therapeutic response and development of new therapeutic modalities .XIST (X-inactive specific transcript) RNA is a long non -coding RNA which plays an important role in inactivation of x\_ chromosome which act as an example for long non \_ coding RNA mediated gene regulation .Very little is known about the role of XIST in human breast cancer and in regulating different response on therapy . the relation between the breast cancer predisposing gene BRCA1 \& XIST has been investigated but still controversial .Loss of X chromosome inactivation (XCI) is observed in breast . some studies provide evedience that BRCA1 Is involved in XIST regulation on the active X chromosome but not its localization .other studies sheds light on a possible mechanism of breast carcinogenesis mediated by XIST misbehaviour .
