KRAS and esophageal squamous cell carcinoma: In colorectal cancer, the concordance rate of the KRAS mutation status between endoscopic biopsy and surgically resected specimens is high [28], similar to that of the PIK3CA mutation status in ESCC demonstrated in the present study, and endoscopic biopsy specimens are used for the molecular analysis of KRAS mutations to evaluate the clinical indications for anti-epidermal growth factor receptor antibody therapy.