Colorectal Cancer

Colon cancer is second only to lung cancer as a cause of cancer death in the United States. The incidence and mortality from this cancer has not changed appreciably during the past several decades. Almost all colorectal cancers are adenocarcinomas, and the disease generally occurs in adults older than 50 years.

Etiology

Most colorectal cancers arise from premalignant adenomatous polyps. Large polyps, especially those larger than 1.5 cm in diameter, are more likely to contain invasive cancer. Although adenomatous polyps are common (present in more than 30% of patients older than 50 years), less than 1% of adenomatous polyps ever become malignant. It is thought that adenomatous polyps require at least 5 years of growth before they become clinically significant. The evolution of normal colonic mucosa to a benign adenomatous polyp that contains cancer and then to life-threatening invasive cancer is associated with a series of genetic events that involve the mutational activation of a proto-oncogene and the loss of several genes that normally suppress tumorigenesis.

Most colorectal cancers appear to be related to diet, with the disease occurring in the greatest incidence among individuals in upper socioeconomic classes living in urban areas. There is a direct correlation between calories consumed, dietary fat and oil, and meat protein. Available data indicate that a high intake of animal fat is the dietary element that is most strongly associated with the risk of colon cancer. As many as 25% of patients with colorectal cancer have a family history of the disease. Inflammatory bowel disease is associated with an increased incidence of colorectal cancer. Cigarette smoking for longer than 35 years appears to increase the risk of colorectal cancer.

Diagnosis

The rationale for colorectal cancer screening is that early detection and removal of localized superficial tumors and precancerous lesions in asymptomatic individuals increases the cure rate. Screening programs (digital rectal examination, examination of the stool for occult blood, colonoscopy) appear to be particularly useful for persons who have first-degree relatives with a history of the disease, especially if these relatives developed the colorectal cancer before 55 years of age. There is evidence that annual or biennial fecal occult blood testing is associated with a decreased incidence of colorectal cancer.

Signs and Symptoms

The presenting signs and symptoms of colorectal cancer reflect the anatomic location of the cancer. Because stool is relatively liquid as it passes into the right colon through the ileocecal valve, tumors in the cecum and ascending colon can become large and markedly narrow the bowel lumen without causing obstructive symptoms. Ascending colon cancers frequently ulcerate, leading to chronic blood loss in the stool. These patients experience symptoms related to anemia, including fatigue and, in some patients, angina pectoris.

Stool becomes more concentrated as it passes into the transverse colon. Transverse colon cancers cause abdominal cramping, occasional bowel obstruction, and even perforation. Abdominal radiographs reveals characteristic abnormalities in the colonic gas pattern, reflecting narrowing of the lumen (“napkin ring lesion”). Colon cancers developing in the rectosigmoid portion of the large intestine result in tenesmus and thinner stools. Anemia is unusual despite the passage of bright red blood from the rectum (often attributable to hemorrhoids).

Colorectal cancers initially spread to regional lymph nodes and then through the portal venous circulation to the liver, which represents the most common visceral site of metastases. Colorectal cancers rarely spread to lung, bone, or brain in the absence of liver metastases. A preoperative increase in the serum concentration of carcinoembryonic antigen suggests that the tumor will recur following surgical resection. Carcinoembryonic antigen is a glycoprotein that is also increased in the presence of other cancers (stomach, pancreas, breast, lung) and nonmalignant conditions (alcoholic liver disease, inflammatory bowel disease, cigarette smoking, pancreatitis).

Treatment

The prognosis for patients with adenocarcinoma of the colorectum depends on the depth of tumor penetration into the bowel wall and the presence or absence of regional lymph node involvement and distant metastases (liver, lung, bone). Radical surgical resection, which includes the blood vessels and lymph nodes draining the involved bowel, offers the best potential for cure. Surgical management of cancers that arise in the distal rectum may necessitate a permanent sigmoid colostomy (abdominoperineal resection). Because most recurrences occur within 3 to 4 years, the cure rate for colorectal cancer is often estimated by 5-year survival rates.

Radiation therapy is a consideration in patients with rectal tumors since the risk of recurrence following surgery is significant. Postoperative radiation therapy causes transient diarrhea and cystitis, but permanent damage to the small intestine and bladder is uncommon. Use of chemotherapy in patients with advanced colorectal cancers rarely results in a satisfactory response.

Management of Anesthesia

Management of anesthesia for surgical resection of colorectal cancers may be influenced by anemia and the effects of metastatic lesions in liver, lung, bone, or brain. Chronic large bowel obstruction probably does not increase the risk of aspiration during induction of anesthesia, although abdominal distention could interfere with adequate ventilation and oxygenation. Blood transfusion during surgical resection of colorectal cancers has been alleged to be associated with a decrease in the length of patient survival. This could reflect immunosuppression produced by transfused blood. For this reason, careful review of the risks and benefits of blood transfusions in these patients is prudent.

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