Malignant tumors of the large intestine

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Management

The only known curative treatment for colonic adenocarcinoma is surgical resection. The prognosis for recurrence after resection depends on the degree of bowel wall invasion by the cancer and the presence of lymph node or distant metastases. If resection is adequate, in the Dukes’ A group only 5% to 10% of patients will have recurrent cancer in contrast to 20% to 30% in the Dukes’ B group and to 50% in the Dukes’ C group with cancer in the colon and 70% with cancer in the rectum.

The incidence and mortality of colorectal cancer has slightly decreased in the United States during the past decade. These observed declines may be due to better diets, removal of premalignant polyps, earlier diagnosis, and improved therapy in varying degrees and contributions.

Cancers in the right colon and left colon require right and left hemicolectomy, respectively. A wide margin should be taken with adequate resection of the mesentery and lymph nodes. Lesions in the rectosigmoid more than 6 to 8 cm from the anal verge may be treated by anterior resection, whereas sizeable cancers below this level require combined abdominal-perineal resection with colostomy. Small low rectal cancers may sometimes be curatively removed by wide local excision. Full-thickness excision, with perirectal lymph nodes if possible, is preferable to electrofulguration for local treatment because it allows pathologic analysis. In unresectable rectal cancer, electrocautery or laser treatment or stent insertion may provide palliation, sometimes precluding the need for colostomy. Resection of colon cancer using laparoscopic “minimally invasive” technique has proved feasible on a trial basis but requires additional follow-up studies.

Irradiation before surgery has been used in treating advanced rectal cancer. An unresectable lesion occasionally becomes resectable after treatment with 2000 to 3000 rad. Some physicians have advocated the routine use of preoperative radiotherapy for rectal lesions, but the results of studies have been conflicting. Postoperative irradiation for patients with rectal cancer at risk for residual disease has been advocated, and some radiation therapists advise a “sandwich” technique combining preoperative and postoperative treatment. In patients with advanced colorectal cancer, after resection of all gross disease, adjuvant therapy with a combination of 5-fluorouracil and levamisole has shown a significantly higher survival rate than in control subjects.

In patients with unresectable colonic cancer, both radiation therapy and chemotherapy have been widely used. Irradiation is usually employed for palliation and shrinkage of tumor masses in the pelvis. Chemotherapy remains unsatisfactory and experimental. 5-Fluorouracil has been the most widely used single agent; only about 15% to 20% of patients respond, most temporarily. Combination chemotherapy and modulation of 5-fluorouracil metabolism has not yet provided a noteworthy advance in colonic carcinoma treatment, although multiple-drug trials are in progress. A combination of radiation therapy and chemotherapy may have some increased benefit over either modality alone.

Infusions of 5-fluorouracil into the hepatic artery or portal vein, or both, have occasionally decreased hepatic metastases when systemic chemotherapy has failed. Patients with liver metastases have been treated with hepatic artery infusion via an implanted pump. A clear advantage over systemic treatment has not been demonstrated. A 5-year survival rate of about 20% has been reported in groups of patients who underwent surgical resection of localized liver metastases.

The judicious use of analgesics, sedatives, antidepressants, blood products, and nutritional supplements by a sympathetic physician can do much to enhance the quality of life for patients with metastatic colonic cancer.

Author: Charles J. Lightdale

BIBLIOGRAPHY

_{Basson MD, Ahlman H, Wangberg B, Modlin IM: Biology and management of the midgut carcinoid, Am J Surg 165:288, 1993.}

DiSario JA, Burt RW, Vargas H et al: Small bowel cancer: epidemiological and clinical characteristics from a population-based registry, Am J Gastroenterol 89:699, 1994.

Fearon ER, Vogelstein B: A genetic model for colorectal tumorogenesis, Cell 61:759, 1990.

Harris AG, Redfern JS: Octreotide treatment of carcinoid syndrome: analysis of published dose-titration data, Aliment Pharmacol Ther 9:387, 1995.

Moertel BC et al: Levamisole and fluorouracil for adjuvant therapy of resected colon carcinoma, N Engl J Med 322:352, 1990.

Rex DK, Rahmani EY, Haseman JH et al: Relative sensitivity of colonoscopy and barium enema for detection of colorectal cancer in clinical practice, Gastroenterology 112:17, 1997.

RELATED STORIES:
Malignant Tumors of the Small Intestine   Hereditary nonpolyposis colorectal carcinoma   Benign tumors of the large intestine   Benign tumors of the small intestine   Carcinoid Tumors of the Small and Large Intestines   Anal Carcinoma

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