A 54 year old woman presents with complaints of abdominal fullness and early satiety. She denies a change in bowel habits and says that constipation is her normal state. A radiographic bowel series shows an "apple core" lesion in her sigmoid colon. Which of the following markers is expected to be elevated in this patient?

CEA is a glycoprotein (200,000 daltons) that is found in the gastrointestinal mucosal cells and pancreatobiliary system secretions. It becomes elevated when breaks in the mucosal basement membrane occur due to tumor growth. Some other conditions can also cause elevations of CEA (e.g., cirrhosis, pancreatitis). The patient described above has colonic carcinoma, and the "apple core" lesion is the classic radiographic finding of this tumor. Although CEA is not used for screening because of the large number of false positives, it can be used to guide treatment in known cases. It returns to normal levels 30-45 days after tumor resection. If it begins to rise again, tumor recurrence is likely. AFP, or alpha-fetoprotein, is an alpha globulin (70,000 daltons) made by the liver and yolk sac of the human fetus. It is elevated with hepatocellular carcinoma and germ cell neoplasms. It is not paicularly specific. hCG, or human chorionic gonadotropin, is a glycoprotein secreted by trophoblastic epithelium of the placenta. It is useful (sensitive and specific) for germ cell tumors of the testis and ovary. LDH, or lactate dehydrogenase, is a very non-specific test that can be elevated in many conditions, including malignancy. Ref: Meric-Bernstam F., Pollock R.E. (2010). Chapter 10. Oncology. In F.C. Brunicardi, D.K. Andersen, T.R. Billiar, D.L. Dunn, J.G. Hunter, J.B. Matthews, R.E. Pollock (Eds), Schwaz's Principles of Surgery, 9e.