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...
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Chapter 087. Gastrointestinal Tract Cancer (Part 16) 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 largebowel. Most such lesions arise in the anal canal, the anatomic area extending fromthe anorectal ring to a zone approximately halfway between the pectinate (ordentate) 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 thesquamous epithelium of the distal anus) are known as basaloid, cuboidal, orcloacogenic tumors; about one-third of anal cancers have this histologic pattern.Malignancies arising distal to the pectinate line have squamous histology, ulceratemore frequently, and constitute ~55% of anal cancers. The prognosis for patientswith basaloid and squamous cell cancers of the anus is identical when correctedfor tumor size and the presence or absence of nodal spread. The development of anal cancer is associated with infection by humanpapillomavirus, the same organism etiologically linked to cervical cancer. Thevirus is sexually transmitted. The infection may lead to anal warts (condylomaaccuminata), which may progress to anal intraepithelial neoplasia and on tosquamous cell carcinoma. The risk for anal cancer is increased among homosexualmales, presumably related to anal intercourse. Anal cancer risk is increased in bothmen and women with AIDS, possibly because their immunosuppressed statepermits more severe papillomavirus infection. Anal cancers occur most commonlyin 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 samplingand 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 ofspread 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 afterbeing managed initially with radiation therapy combined with chemotherapy. Further Readings Crump W et al: Lymphoma of the gastrointestinal tract. Semin Oncol26:324, 1999 [PMID: 10375089] Demetri GD et al: Efficacy and safety of imatinib mesylate in advancedgastrointestinal 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 Med348:919, 2003 [PMID: 12621137] Meyerhardt JA, Mayer RJ: Systemic therapy for colorectal cancer. N Engl JMed 352:476, 2005 [PMID: 15689586] Rostrum A et al: Nonsteroidal anti-inflammatory drugs andcyclooxygenase-2 inhibitors for primary prevention of colorectal cancer: Asystematic review prepared for the US Preventive Services Task Force. Ann InternMed 146:376, 2007 Ryan DP et al: Carcinoma of the anal canal. N Engl J Med 342:792, 2000[PMID: 10717015] Spechler SJ: Barretts esophagus. N Engl J Med 346:836, 2002 [PMID:11893796] Uemura N et al: Helicobacter pylori infection and the development ofgastric 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 J57:168, 2007