A 45-year-old businesswoman arrives in your office with vague abdominal complaints. She has noticed melenic stool. Upon performing a sigmoidoscopy, you find a 4-cm mass in the upper colon. You should immediately order a blood test for which of the following tumor markers?
a-Fetoprotein Anti-tumor antibody Antitumor light chains Carcinoembryonic antigen (CEA)