CEACAM5 and gastric cancer: Although their probe was able to visualize the tumors, background signals (signals from surrounding normal tissue) were high.45 Despite the limited utility of serum CEA levels to detect gastric cancer upon initial diagnosis or at the time of recurrence, 74.5–90% of gastric cancers have been shown to express CEA by immunohistochemistry.26,27,46–48 Therefore, CEA is an excellent target for fluorescence labeling of gastric cancer.