Commercial Carcinoembryonic Antigen Assays To the Editor:

one of the first known tumor mark-ers, is still the most useful clinical marker to aid in the diagnosis and monitoring of colorectal cancer. Many commercial assays are avail-able for measuring CEA, but their practical use is complicated by the molecular heterogeneity of CEA. CEA is a heavily glycosylated protein of the immunoglobulin gene super-family and has several related anti-gens such as nonspecific cross-reacting antigen (NCA), NCA-2, and normal fecal antigen. Previous investigations have indicated tha