CEACAM5 and colonic neoplasm: Reducing the incubation time of the primary antibody and using different blocking reagents allowed differential detection of CEA expression between the strongly positive HT29 and weakly positive HCT 116 colon cancer cells (Supplemental Figure S9), which more closely matched the results obtained with unconjugated primary antibody and fluorescence-labeled secondary antibody (Supplemental Figure S8).