These tumors are relatively rare, comprising only 1-2% of all cancers of the anus and large intestine. Squamous cancers make up the majority of anal cancers. Squamous cancer involving the anal canal may be subclassified as transitional and cloacogenic carcinoma; however, these are treated similarly. Anal cancer is increased among people practicing receptive anal intercourse and those with a history of other sexually transmitted diseases.

In over 80% of cases, HPV may be detected, suggesting that this virus may be a causal factor. Anal cancer is increased in HIV-infected individuals. Combined HIV and HPV infection markedly increases the risk of anal carcinoma. Bleeding, pain, and local tumor are the commonest symptoms. The lesion is often confused with hemorrhoids or other common anal disorders. These tumors tend to become annular, invade the sphincter, and spread upward via the lymphatics into the perirectal mesenteric lymphatic nodes.

Treatment depends on the tumor stage.

MR scan and endoluminal ultrasound assist in determining the depth of penetration and local spread. Small (

< 3 cm) superficial lesions of the perianal skin may be treated with wide local excision. Squamous cancer of the anal canal and large perianal tumors invading the sphincter or rectum are treated with combined-modality therapy that includes external radiation with simultaneous chemotherapy (fluorouracil and either mitomycin or cisplatin). Local control is achieved in 80% of patients. Radical surgery (abdominoperineal resection) is reserved for patients who fail chemotherapy and radiation therapy. The 5-year survival rate is 60-70% for localized tumors and over 25% for metastatic (stage IV) disease.

Hope S. Rugo, MD
References

• Anal Cancer (PDQ) Treatment—National Cancer Institute—Cancer Net: http://cancernet.nci.nih.gov.
• Peiffert D et al. Cancer of the anal canal. Gastroenterol Clin Biol. 2006 Sep;30 Spec No 2:2S52-2S56. [PMID: 17151563]
• Welton ML et al. The etiology and epidemiology of anal cancer. Surg Oncol Clin N Am. 2004 Apr;13(2):263-75. [PMID: 15137956]