In view of the history of rectal bleeding, weight loss, and the patient’s age, his physician suspected that he might have col- orectal cancer and requested the patient to submit three con- secutive daily specimens of feces for the fecal occult blood test. Shortly thereafter the physician received a report indicating that the results were positive. He also ordered a complete blood count and estimations of levels of serum iron, iron-binding capacity, and ferritin. The results showed a microcytic anemia (see Chapter 52), often found in patients with colorectal cancer because of bleeding from the tumor. A rectal examination was negative. No abnormalities were noted in chest x-rays.The physician arranged a consult 4 days later with a gas- troenterologist. Colonoscopy was performed 1 week later. This revealed the presence of a moderately large tumor (approxi- mately 5 6 cm) in the middle of the transverse colon. Mea- surement of carcinoembryonic antigen (CEA), a biomarker for colorectal cancer (see below for further comments and also Chapter 7), was ordered. It was elevated (20 μg/L, normal 0–3 μg/L). Surgery was scheduled 2 weeks later, when the tumor was resected and end-to-end anastomosis performed. The regional lymph nodes were also excised and submitted along with the tumor specimen to the pathology lab. No local invasion by the tumor was noted, and no tumor was visible elsewhere in the abdomen, including the liver. The subsequent pathology report described the tumor as a relatively well-dif- ferentiated adenocarcinoma, invading the muscular mucosa. No tumor cells were noted in the lymph glands; no distant me- tastases were noted at the time of surgery. The TNM stage was T1N0M0 (cancer limited to the mucosa and submucosa, with an approximate 5-year survival rate of >90% [T = tumor, N = nodes, M = metastases]). (The interested reader should check the staging of tumors of the large intestine in a textbook of pa- thology.) In view of these findings, no chemotherapy or radia- tion therapy was considered necessary. Determination of CEA several weeks after surgery showed it had declined to normal levels. The patient was advised to return for follow-up at regu-