Progression of breast cancer is associated with claudin-1 expression affecting Ephrin B1 and EpCAM.18Claudin-1 also shows exhibition of antiapoptotic effects in some breast cancer cell lines, like MCF-7.19However, some studies have shown a correlation of increased malignancy, invasiveness, and recurrence of breast cancer with total or partial loss of claudin-1 expression.20 This evidence concerns the gene EFNB1 and breast cancer.