Anal cancer

A squamous cell carcinoma of the anus visible

Symptoms of anal cancer can include pain or pressure in the anus or rectum, a change in bowel habits, a lump near the anus, rectal bleeding, itching or discharge. Bleeding may be severe.[7][8]

• Human papillomavirus: 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.[9] In another study done, high-risk types of HPV, notably HPV-16, were detected in 84 percent of anal cancer specimens examined.[10] Based on the study in Denmark and Sweden, Parkin estimated that 90% of anal cancers are attributable to HPV.[11]
• Sexual activity: Due to increased risk of exposure to HPV, having multiple sex partners and receptive anal intercourse greatly increases the likelihood of developing anal cancer, for men and women.[12][13][14]
• Smoking: Current smokers are several times more likely to develop anal cancer compared with nonsmokers.[14] Epidemiologist Janet Daling, Ph.D., a member of Fred Hutchinson's Public Health Sciences Division, and her team found that smoking appears to play a significant role in anal-cancer development that is independent of other behavioral risk factors, such as sexual activity. More than half of the anal-cancer patients studied were current smokers at the time of diagnosis, as compared to a smoking rate of about 23 percent among the controls. "Current smoking is a very important promoter of the disease," said Daling. "There's a fourfold increase in risk if you're a current smoker, regardless of whether you're male or female." They explained that the mechanism behind smoking and anal-cancer development is unknown, but researchers speculate that smoking interferes with a process called apoptosis, or programmed cell death, which helps rid the body of abnormal cells that could turn cancerous. Another possibility is that smoking suppresses the immune system, which can decrease the body's ability to clear persistent infection or abnormal cells.[12]
• Immunosuppression, which is often associated with HIV infection.[14]
• A history of cervical, vaginal or vulval cancers[15]
• Cloacogenic. Cloacogenic carcinoma is a rare tumor of the anorectal region originating from a persistent remnant of the cloacal membrane of the embryo. The tumor accounts for 2–3% of anorectal carcinomas and occurs more than twice as often in women.[16]

Most anal cancers are squamous cell carcinomas (epidermoid carcinomas), that arises near the squamocolumnar junction. It may be keratinizing (basaloid) or non-keratinizing (cloacogenic).[17]

Other types of anal cancer are adenocarcinoma, lymphoma, sarcoma or melanoma.

• 
  Stage 1 anal cancer
• 
  Stage 2 anal cancer
• 
  Stage 3 anal cancer
• 
  Stage 4 anal cancer

Since many, if not most, anal cancers derive from HPV infections, and since the HPV vaccine before exposure to HPV prevents infection by some strains of the virus and has been shown to reduce the incidence of potentially precancerous lesions,[20] scientists surmise that HPV vaccination may reduce the incidence of anal cancer.[21] The efficacy of the vaccine against HPV types 16 and 18 in naive women ≤26 years old has been shown to be between 91-100% but is lower when individuals are vaccinated irrespective of baseline HPV infection at 76%.[22]

In 2010, Gardasil was approved in the US to prevent anal cancer and pre-cancerous lesions in males and females aged 9 to 26 years. The vaccine has been used before to help prevent cervical, vulvar, and vaginal cancer, and associated lesions caused by HPV types 6, 11, 16, and 18 in women.[23]

As the incidence of anal cancer has increased in recent years, screening and early detection of anal intraepithelial neoplasia (AIN) has become a necessity in patients at risk. This screening detects premalignant lesions, which are highly prevalents, and improves the staging of lesions after treatment.[24]

Anal Pap smears similar to those used in cervical cancer screening have been studied for early detection of anal cancer in high-risk individuals.[25] In 2011, an HIV clinic implemented a program to enhance access to anal cancer screening for HIV-positive men. Nurse practitioners perform anal Papanicolaou screening, and men with abnormal results receive further evaluation with high-resolution anoscopy. The program has helped identify many precancerous growths, allowing them to be safely removed.[26] A similar study was performed in women with a history of cervical cancer or high-grade cervical intraepithelial neoplasia. More than 30% had abnormal anal Pap smears and one third of those already had anal intraepithelial neoplasia.[27]

Median survival rates for people with distant metastases range from 8 to 34 months.[31] Surgical resection with permanent colostomies was the standard treatment until the 1970s, yielding 5-year overall survival of approximately 50%. The best overall survival rates are seen after combined radiation therapy combined with chemotherapy (5-FU + Mitomycin) in people with T2N0 and T3N0 categories of disease (5-y overall survival: 82%). The 5-year overall survival rates of patients with T4 with no involved lymph nodes, T3 with involved lymph nodes, and T4 with involved lymph nodes disease after the combined treatment is 57%, 57%, and 42%, respectively.[33][34]

Worldwide in 2002 there were an estimated 30,400 new cases of anal cancer.[11] With approximately equal fractions in the developing (15,900) and developed (14,500) countries.[11] An estimated 90% (27,400) were attributable to human papillomavirus (HPV).[11]

• American Cancer Society: Anal Cancer
• Anal cancer information from Cancer Research UK
• National Cancer Institute: Anal cancer