Consistently, we found that the protein levels of LKB1 and its downstream target P27 were markedly reduced in a panel of ESCC cells compared to normal esophageal epithelial cells (NE2 and NE3), which is opposite to the high expression of RBM4 in ESCC cells (Supplementary Fig. 6b). Here, STK11 is linked to esophageal squamous cell carcinoma.