GAPDH and neoplasm: circRNA expression level was determined using quantitative real-time polymerase chain reaction (qRT-PCR) or RNA sequencing, and the reference genes included GAPDH,[10–17,19,20] 18S rRNA,[9] and U6.[18] Six types of circRNAs were recognized as tumor promoters,[12,15,16,18,20] and 7 as tumor suppressors.[9–11,13,14,17,19] Survival analysis was available in 2 studies, and 3 articles contained data on HR and 95% CI, whereas the HR values in the remaining 4 articles were unclear and calculated indirectly.