Improved median PFS (3.4 vs. 1.4 months, P = 0.006) and OS (8.0 vs. 4.2 months, P = 0.027) were associated with TP53 mutation abundance of < 10%....SCT200 monotherapy as second- or further-line for advanced ESCC showed favorable efficacy, with an acceptable safety profile. TP53 mutation abundance might serve as potential predictive biomarkers.