The adenocarcinoma (AC)-squamous cell carcinoma (SCC) discriminative surface in the use of KRT6A, KRT6B, and KRT6C as a signature is shown. The classification accuracy achieved by this signature was 90.2%, accounting for 95% of the accuracy of the entire 25-gene signature. Simulating the possible expression levels of the 3 genes generated a nonlinear discriminative surface, in which the region below it belonged to AC, and the region above belonged to SCC