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Anal cancer
| Last updated: 21.12.05 |
Since potent and effective anti-HIV treatment became available (often referred to as highly active antiretroviral therapy, or HAART for short) the number of cases of the AIDS-defining cancers such as Kaposi’s sarcoma and non-Hodgkin’s lymphoma have fallen, and the outlook for people diagnosed with these cancers has improved.
There is some evidence, however, that some cancers not traditionally regarded as being AIDS-defining (occurring when a person has a very weak immune system) have become more common in HIV-positive people since HAART became available. One of these is anal cancer and doctors in the UK, and many other countries where HAART is available, have noted an increase in the number of cases of anal cancer in HIV-positive people, particularly among gay men.
Human papilloma virus (HPV), the cause of genital and anal warts is the underlying cause of anal cancer, and infection with HPV is widespread amongst gay men in general, and is particularly high amongst HIV-positive gay men. Infection with HPV in the anus has also been associated with the development of anal cancer in HIV-positive women.
It is thought that the reason why there has been an increase in the number of cases of anal cancer since HAART became available is because people with HIV are living longer.
Pre-cancerous lesions
The overwhelming majority of people with anal HPV infection will not go on to develop anal cancer.
Some studies suggest that people with anal HPV whose lowest ever CD4 cell count was below 200 may be at more risk of developing abnormal cells in their anus. Certain strains of HPV seem more likely to cause genital cancers than others, but many HIV-positive gay men are often infected with multiple strains of HPV, including both high and lower risk types of HPV.
Before cancer develops, cells in the anus will go through a number of changes over many years and pre-cancerous lesions called AIN (anal intraepithelial neoplasmia) may develop. AIN lesions are graded AIN I, AIN II, and AIN III depending on their stage.
Monitoring
Having a regular sexual health screen which involves an examination of the anus and rectum (called a proctological examination) will mean that anal warts and lesions can be detected promptly. There is no link between visible anal warts and anal cancer. The strains of HPV which can cause cancer do not cause a wart-like growth to develop. Nevertheless, they can cause lesions. It is worth having a regular anal examination even if you do not have receptive anal sex, or if you always use condoms for anal sex. Studies have found that men and women who have never had anal sex, or always have protected anal sex, nevertheless have anal warts. This could be because HPV can be spread by touch.
Make sure that you tell your doctor if you notice any unusual symptoms in your rectum or anus.
Some HIV clinics are looking at the value of regularly screening individuals with anal HPV for precancerous cell. This involves using a test very similar to the PAP (Papanicolaou) smear used to detect pre-cancerous cervical cells in women. Cells are scraped from the lining of the anus (which can be uncomfortable), and then examined for signs of abnormalities. Anal PAP smears are not 100% accurate. The anus can be examined in more detail using a magnifying instrument during a procedure called an anoscopy. During this procedure small tissue samples from the anus can be removed – biopsied – and examined under a microscope to see if potentially cancerous changes to cells have occurred.
Treatment
Often the immune system successfully clears infection with HPV. Treatment with HAART can restore the immune system and improve its ability to fight infections, including HPV. HAART, however, does not have a direct effective against HPV, and cases of anal cancer have occurred in people with good CD4 cell counts and undetectable viral loads.
Imiquimod cream has been shown to be an effective treatment for anal and genital warts and works against HPV.
Anal cancer is usually treated aggressively with a combination of chemotherapy and radiotherapy. The cure rate is approximately 60%, but the treatment has very unpleasant side-effects.
Surgery can be used to remove precancerous and cancerous cells from the anus. However, in many cases the precancerous or cancerous cells may recur.
Remember, anal cancer is rare, even amongst individuals with anal HPV infection, and the sooner any potentially cancerous changes are detected and treated occur the better. Speak to your doctor or a member of your healthcare team if you have any concerns.