The circular RNA MTO1 (circMTO1) originates from exons 2 and 3 of the mitochondrial tRNA translation optimization 1 (MTO1) gene with a 318bp splice length (Figure 2), and was first reported in hepatocellular carcinoma (Han et al., 2017; Fan et al., 2019). This evidence concerns the gene MTO1 and hepatocellular carcinoma.