PYCR1 and esophageal squamous cell carcinoma: In ESCC tissues, circ_0000705 expression manifested a negative and significant correlation with miR-621 (r =  − 0.689, P < 0.001; Fig. 7E), and a positive and significant correlation with PYCR1 mRNA (r = 0.692, P < 0.001; Fig. 7F).