Forty-seven percent of the patients had elevated CEA levels before nCRT, and elevated pre-nCRT CEA was independently associated with decreased pCR (odds ratio = 0.65, 95% CI = 0.52–0.77, p < 0.001), reduced pathological tumor regression (odds ratio = 0.74, 95% CI = 0.67–0.70, p < 0.001), reduced tumor downstaging (odds ratio = 0.77, 95% CI = 0.63–0.92, p < 0.001), and overall survival (hazard ratio = 1.45, 95% CI = 1.34–1.58, p < 0.001). This evidence concerns the gene CEACAM5 and neoplasm.