Anal Cancer Risk Factors and Screening

Risk Factors & Screening

Anal cancer is much less common than colorectal cancer and is unique from it in a variety of ways. Although only 5290 patients were diagnosed with anal cancer the US in 2009 [1] , the incidence seems to be rising likely due to the increasing prevalence of the two main risk factors, HPV (human papilloma virus) infection, and HIV (human immunodeficiency virus) infections. This is one kind of cancer that is largely due to a sexually transmitted infection. Men who have sex with men seem to have the greatest risk, especially if they are HIV+ and have had HIV for a long time [2]. Patients on chronic immunosuppression for organ transplants also carry an increased chance of this malignancy.

HPV is the same virus that causes cervical cancer in women. If you are a woman who has had known HPV, cervical cancer, vaginal or anal warts, or several abnormal Pap smears, then the risk of anal cancer is also increased. It is not necessary to have had anal sex to have the virus spread to the skin around the anal opening. If you are a man with a history of genital or anal warts, you also have increased risk. It is highly recommended that anal warts be removed to reduce the chance of evolving into cancer. Small ones can be frozen off with liquid nitrogen or “burned” off with bichoroacetic acid right in the office with minimal discomfort. Larger and multiple areas of anal warts require anesthesia to excise and burn these off with electrocautery.

There are particular strains of HPV that seem more likely to lead to cancer than others, those being subtypes 16, 18, 31, 33 and 35 [3]. Although some anal cancers appear to be HPV negative, the vast majority are associated with HPV infection. Optimism exists, that vaccination for HPV before sexual activity starts may reduce the incidence of cervical and anal cancer.

Screening programs exist in places like San Francisco and New York where there are large numbers of HIV+ men, but practicality precludes their existence in other places. Techniques include anal Pap smears and high resolution anoscopy, but it is hard to prove the benefit on a broader scale. Most colorectal surgeons do a very careful visual and digital exam with anoscopy with appropriate biopsy of suspicious lesions.

The symptoms of anal cancer unfortunately are often confused for hemorrhoids. Therefore, it is often seen that people are treating themselves with over the counter remedies for months and often seeing their primary physician and continuing with prescription strength hemorrhoidal treatments, before recognition that referral to a colorectal specialist is warranted. Pain and bleeding are the most common symptoms. A mass may be felt when wiping that is tender and bleeds easily, but some anal cancers are inside the anal canal and not visible at all. Being examined by a colorectal surgeon will entail digital rectal exam and likely anoscopy that will identify if this is consistent with anal cancer. It may be impossible to differentiate an anal cancer from a distal rectal cancer, so biopsy is very helpful. Unlike rectal cancer, which is an adenocarcinoma (arising from mucosa of the digestive system), anal cancer is an epidermoid, or squamous cell cancer which arises from skin cells.

[1] Jamal, et al.  Cancer Statistics 2009. CA Cancer J Clin. 59:225-249, 2009
[2] Daling JR, Madelieine MM, Johnson LG.  Human papilloma virus, smoking, sexual practices in the etiology of anal cancer. NEJM 337:1350-58, 1997
[3] Ryan DP, Compton CC, Mayer RJ: Carcinoma of the anal canal. NEJM 342:792-800, 2000

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