SPINK1 and breast cancer: For example, circ-0000502, circ-PRMT5, circ-SPINK1, circ-0103552 and ciRS-7 were reported to be promising prognostic biomarkers in osteosarcoma [31], bladder cancer [32], hepatocellular carcinoma [33], breast cancer [34] and colorectal cancer [35], respectively.