As a result, the red fluorescent signals from the Cy5-labeled novel aptamer (6) were strong in CEA-positive HT-29 cells (Figure 6b), and no signal was observed in the HeLa S3 cells that were used as a negative control (Figure 6d), further indicating that the novel aptamer (6) can bind to CEA-positive colorectal cancer cells in vitro. This evidence concerns the gene CEACAM5 and colorectal cancer.