Anal cancer

Anal cancer is a type of cancer which arises from the anus, the distal orifice of the gastrointestinal tract. It is a distinct entity from the more common colorectal cancer. The etiology, risk factors, clinical progression, staging, and treatment are all different. Anal cancer is typically a squamous cell carcinoma that arises near the squamocolumnar junction.

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Risk factors

• Human papillomavirus (HPV) infection: An examination of squamous cell carcinoma tumor tissues from patients in Denmark and Sweden showed a high proportion of anal cancers to be positive for the types of HPV that are also associated with high risk of cervical cancer (90% of the tumors from women, 100% of the tumors from homosexual men, and 58% of tumors from heterosexual men).^[1] In another study done, high-risk types of HPV, notably HPV-16, were detected in 84 percent of anal cancer specimens examined.^[2]

• Sexual activity: Having multiple sex partners or having anal sex, due to the increased risk of exposure to the HPV virus.^[3]

• Smoking: Current smokers are several times more likely to develop anal cancer compared with nonsmokers.^[3]

• Immunosuppression, which is often associated with HIV infection.^[3]

Prevention

Since many, if not most, anal cancers derive from Human Papilloma Virus infections, and since the HPV vaccine prevents infection by several strains of the virus, scientists surmise that HPV vaccination will prevent anal cancer. ^[4]

Screening

Anal pap smears similar to those used in cervical cancer screening have been studied experimentally for early detection of anal cancer in high-risk individuals.^[5][6]

Treatment

Localized disease

Anal cancer is most effectively treated with surgery, and in early stage disease (i.e., localized cancer of the anus without metastasis to the inguinal lymph nodes), surgery is often curative. The difficulty with surgery has been the necessity of removing the anal sphincter, with concomitant fecal incontinence. For this reason, many patients with anal cancer have required permanent colostomies.

In more recent years, physicians have employed a combination strategy including chemotherapy and radiation treatments to reduce the necessity of debilitating surgery. This "combined modality" approach has led to the increased preservation of an intact anal sphincter, and therefore improved quality of life after definitive treatment. Survival and cure rates are excellent, and many patients are left with a functional sphincter. Some patients have fecal incontinence after combined chemotherapy and radiation. Biopsies to document disease regression after chemotherapy and radiation were commonly advised, but are not as frequent any longer. Current chemotherapy active in anal cancer includes cisplatin and 5-FU; mitomycin has also been used, but is associated with increased toxicity.

Metastatic or recurrent disease

Up to 10% of patients treated for anal cancer will develop distant metastatic disease. Metastatic or recurrent anal cancer is difficult to treat, and usually requires chemotherapy. Radiation is also employed to palliate specific locations of disease that may be causing symptoms. Chemotherapy commonly used is similar to other squamous cell epithelial neoplasms, such as platinum analogues, anthracyclines such as doxorubicin, and antimetabolites such as 5-FU and capecitabine.

Prognosis

See also

• Anal warts

References