XIST and breast carcinoma: As an example, higher expression of XIST has been linked to breast cancer pathogenesis and chemoresistance (Table 1) [133,210] and here the very low expression of XIST could at least partly underlie the very low risk of breast cancer among TS women and, vice versa, the higher XIST expression in KS men involved in the increased breast cancer incidence [211,212], which to date has not been explained convincingly by other data.