There were no significant differences between the training cohort and external validation cohort in gender, age, mrT Stage after nCRT, CEA level before nCRT, tumor differentiation, tumor location, or chemoradiotherapy regimen (p = 0.686, 0.417, 0.349, 0.236, 0.785, 0.675, and 0.669, respectively; Table 2). The gene discussed is CEACAM5; the disease is neoplasm.