CEACAM5 and rectal cancer: What is more, several studies had reported that rectal cancer has less microsatellite instability and fewer BRAF mutations than colon cancer does.24–26 Different gene expression profiles between colon and rectal cancer have been reported.27,28 So another hypothesis is that maybe in rectal cancer, CA19-9 plays a more important role than CEA does, whereas in colon rectal CEA is more important.