HOTAIR and cancer: As an emerging hot spot of cancer research, numerous cancer-specific lncRNAs have been identified, among which several have been validated as biomarkers for metastasis or metabolism, such as metastasis associated long antisense transcript 1 (MALAT-1) [9], prostate cancer gene expression marker 1 (PCGEM1) [10] and HOX transcript antisense RNA (HOTAIR) [11].