CEACAM5 and neoplasm: The change of serum CEA levels before and after CRT seems to be more obvious in patients with pre-CRT serum CEA ≥6 ng/ml than those with normal levels (mean CEA ratio ± standard deviation, 0.36 ± 0.25 vs. 0.87 ± 0.30; p < 0.001); accordingly, a low post-CRT CEA level or CEA ratio may represent a marked reduction of tumor burden after CRT, especially when pre-CRT CEA levels are higher than the normal limit.