Due to its high stability, circRNA is an excellent biomarker for human diseases, especially cancer [25]; examples include circ-SMARCA5 as a biomarker for hepatocellular carcinoma [26], circ-ANKS1B for breast cancer [27], circ-UBXN7 for bladder cancer [28] and circ-LMTK2 for gastric cancer [29]. This evidence concerns the gene LMTK2 and breast cancer.