HIF1A and cancer: In addition, recent data demonstrated that HIF-1α can directly regulate circRNAs at the transcriptional level [51,52] and that HIF-induced circRNAs may promote cancer growth as demonstrated in bladder [53]; however, unlike miRNAs and lncRNAs, the mechanisms of HIF-mediated circRNAs expression have been less investigated and will not be further addressed in this review.