It was reported that knockdown of HOTAIR sensitized HepG2 cells to TNF-α, doxorubicin and cisplatin, and the level of HOTAIR declined markedly in HeLa and MCF-7 cells when apoptosis induced by bleomycin happened.12, 13 Moreover, HOTAIR knockdown caused apoptosis in multiple cancer cell lines, and ectopic expression of HOTAIR reduced that.9, 14, 15, 16 Tumor shrinking effect of targeting HOTAIR has been validated in a mouse xenograft model.16 However, there is not a study reporting why HOTAIR knockdown leads to cancer cell apoptosis. This evidence concerns the gene HOTAIR and cancer.