NRN1 and esophageal cancer: Based on “BRCAness” principle, our recent study found that methylation of NRN1 was a novel synthetic lethal marker for PI3K-Akt-mTOR and ATR inhibitors in human esophageal cancer (McLornan et al., 2014; Lord and Ashworth, 2016, 2017; Du et al., 2021).