CD99 and cancer: Indeed, chemoresistant cell lines share a higher level of proteins preferentially expressed by cancer cells with stem-like characteristics and/or that have undergone EMT transition, such as CD44 [54], PDGFRβ [46,50], CD99 [52,53], vimentin [51], integrin αv and integrin β1 [47,48], and lower levels of ZO-1 chosen as epithelial marker [55], compared to parental MDA-MB-231 cells.