HX103, an epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitor (TKI)-based fluorogenic probe, exhibits selective inhibition towards various EGFR mutations, including EGFR 19 del, EGFR L858R, EGFR wild type, and EGFR T790M, with respective IC50 values of 1.3, 1.5, 4.0, and 977 nM. It is utilized for quantifying active-EGFR to foresee agent sensitivity in NSCLC (non-small cell lung cancer) patients harboring EGFR-activating mutations [1].