KRT1 and digestive system neoplasm: Recently, some clinicians have employed a combination of CEA, CA19-9, cytokeratin-1 (CK-1), CA72-4 and mucin-1 (MUC-1) to predict unfavorable outcomes in gastrointestinal tumors, which has improved the sensitivity and specificity of tumor surveillance while also evaluating tumor stage and metastasis (Pua et al., 2020).