Chapter 087. Gastrointestinal Tract Cancer (Part 16)

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Cancers of the Anus Cancers of the anus account for 1–2% of the malignant tumors of the large bowel. Most such lesions arise in the anal canal, the anatomic area extending from the anorectal ring to a zone approximately halfway between the pectinate (or dentate) line and the anal verge. Carcinomas arising proximal to the pectinate line (i.e., in the transitional zone between the glandular mucosa of the rectum and the squamous epithelium of the distal anus) are known as basaloid, cuboidal, or cloacogenic tumors; about one-third of anal cancers have this histologic pattern. Malignancies arising distal to the...

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Chapter 087. Gastrointestinal Tract Cancer (Part 16) Cancers of the Anus Cancers of the anus account for 1–2% of the malignant tumors of the large bowel. Most such lesions arise in the anal canal, the anatomic area extending from the anorectal ring to a zone approximately halfway between the pectinate (or dentate) line and the anal verge. Carcinomas arising proximal to the pectinate line (i.e., in the transitional zone between the glandular mucosa of the rectum and the squamous epithelium of the distal anus) are known as basaloid, cuboidal, or cloacogenic tumors; about one-third of anal cancers have this histologic pattern. Malignancies arising distal to the pectinate line have squamous histology, ulcerate more frequently, and constitute ~55% of anal cancers. The prognosis for patients
with basaloid and squamous cell cancers of the anus is identical when corrected for tumor size and the presence or absence of nodal spread. The development of anal cancer is associated with infection by human papillomavirus, the same organism etiologically linked to cervical cancer. The virus is sexually transmitted. The infection may lead to anal warts (condyloma accuminata), which may progress to anal intraepithelial neoplasia and on to squamous cell carcinoma. The risk for anal cancer is increased among homosexual males, presumably related to anal intercourse. Anal cancer risk is increased in both men and women with AIDS, possibly because their immunosuppressed state permits more severe papillomavirus infection. Anal cancers occur most commonly in middle-aged persons and are more frequent in women than men. At diagnosis, patients may experience bleeding, pain, sensation of a perianal mass, and pruritus. Radical surgery (abdominal-perineal resection with lymph node sampling and a permanent colostomy) was once the treatment of choice for this tumor type. The 5-year survival rate after such a procedure was 55–70% in the absence of spread to regional lymph nodes and 80% of patients whose initial lesion was
reserved for the minority of individuals who are found to have residual tumor after being managed initially with radiation therapy combined with chemotherapy. Further Readings Crump W et al: Lymphoma of the gastrointestinal tract. Semin Oncol 26:324, 1999 [PMID: 10375089] Demetri GD et al: Efficacy and safety of imatinib mesylate in advanced gastrointestinal stromal tumors. N Engl J Med 347:472, 2002 [PMID: 12181401] Enzinger PC, Mayer RJ: Esophageal cancer. N Engl J Med 349:2241, 2003 [PMID: 14657432] Hohenberger P, Gretschel S: Gastric cancer. Lancet 362:305, 2003 [PMID: 12892963] Lynch HT, De la Chapelle A: Hereditary colorectal cancer. N Engl J Med 348:919, 2003 [PMID: 12621137] Meyerhardt JA, Mayer RJ: Systemic therapy for colorectal cancer. N Engl J
Med 352:476, 2005 [PMID: 15689586] Rostrum A et al: Nonsteroidal anti-inflammatory drugs and cyclooxygenase-2 inhibitors for primary prevention of colorectal cancer: A systematic review prepared for the US Preventive Services Task Force. Ann Intern Med 146:376, 2007 Ryan DP et al: Carcinoma of the anal canal. N Engl J Med 342:792, 2000 [PMID: 10717015] Spechler SJ: Barrett's esophagus. N Engl J Med 346:836, 2002 [PMID: 11893796] Uemura N et al: Helicobacter pylori infection and the development of gastric cancer. N Engl J Med 345:784, 2001 [PMID: 11556297] Walsh JME, Terdiman JP: Colorectal cancer screening. JAMA 289:1288, 2003 [PMID: 12633191] Weitz J et al: Colorectal cancer. Lancet 365:153, 2005 [PMID: 15639298]
Wolan BM et al: Adjuvant treatment of colorectal cancer. CA Cancer Clin J 57:168, 2007