December 19, 2012
HIV attacks the immune system, causing it to become increasingly weak and dysfunctional. Treatment with combinations of potent anti-HIV drugs (commonly called ART or HAART) greatly reduces production of HIV in the body. As less HIV is produced, the immune system can begin repairs. These repairs are generally sufficient to keep AIDS-related infections at bay. However, because defects in immunity persist, there is an elevated risk for certain cancers in some ART users. The degree of this elevated cancer risk varies from one HIV-positive person to another and arises from a complex intersection of factors, likely including some of the following:
Due to similar routes of transmission, some HIV-positive people are also infected with other viruses. Some of these viruses can cause cells to develop abnormally. Such abnormal cells can transform into pre-cancers and, in some cases, even cancer. Some viruses with this cancer-causing potential include the following:
Researchers have found that in the time before ART became available, cases of anal cancer were twice as high among HIV-positive men who have sex with men (MSM) compared to HIV-negative MSM.
Furthermore, compared to the average HIV-negative man, the relative risk of anal cancer is many times greater for HIV-positive men who are not MSM (37-fold) and even greater for HIV-positive MSM (60-fold).
Some studies have found no reduction in the risk of anal cancer among HIV-positive people in the current era in places where ART is widely available. In contrast, two studies suggest a decreased risk of this cancer with prolonged use of ART. However, what all studies of anal cancer in high-income countries in the current era have in common is that cases appear to be increasing compared to the time before ART was available.
Most studies comparing anal cancer risk among HIV-positive people have involved a relatively small number of cases -- between 18 and 80. Such studies did not generally account for factors such as the following:
Also, most of these studies could not clearly conclude whether anal cancer was occurring at a younger age in HIV-positive people compared to HIV-negative people.
To address this and other issues, researchers in France conducted an analysis of their database, which has collected health-related information from nearly 110,000 HIV-positive people. The researchers also compared the data on HIV-positive people with that from HIV-negative people with anal cancer.
Surprisingly, in their report, the French team found no significant difference in the relative risk for anal cancer in the pre-HAART era (1992 to 1996) and the HAART-era (1997 to 2008). Furthermore, no differences in anal cancer risk were found in the early HAART era (1997 to 2000) and the later HAART era (2005 to 2008). Additional findings from this important study appear later in this CATIE News bulletin, along with steps on how to reduce anal cancer risk.
The French Hospital Database has collected health-related information on 109,771 HIV-positive people from 69 clinics in hospitals across France.
For purposes of comparison, the researchers obtained information on anal cancer cases in HIV-negative people from a database called FRANCIM (France-cancer-incidence et mortalité). That database contained information collected from about 12 million people.
In the present study, the analysis on anal cancer focused on the period between January 1992 and December 2008.
Over the 16 years of the study, cases of anal cancer were distributed as follows:
Rates of new cases of anal cancer were highest among HIV-positive MSM, followed by what the researchers called "other" HIV-positive men, and then HIV-positive women.
Anal cancer was more likely to occur among HIV-positive people with the following profile:
The risk of anal cancer nearly tripled in the current era compared to the pre-HAART era. This likely arose because of differences in survival. For instance, in the pre-HAART era, participants were much more likely to die at a younger age from complications stemming from an AIDS-related infection. In the HAART era, in high-income countries, such complications are no longer common. This means that people live longer with both HIV and HPV infection, which allows more time for tumours to develop. In the present era, thanks to HAART, HIV-positive people likely feel better, and so interest in sex returns. This leads to resurgence in sex, which may also mean more exposure to strains of HPV that are associated with tumours.
Having a high CD4+ cell count did not seem to be protective from anal cancer because cases of anal cancer were documented even among HIV-positive people whose CD4+ counts were greater than 500 cells. Furthermore, among participants whose CD4+ cell counts were greater than 500 cells for two years before the diagnosis of anal cancer, their risk for this cancer was 20-fold greater than among HIV-negative people.
The researchers found that all sub-groups of HIV-positive people experienced an increase in diagnoses of anal cancer after ART became available. Although the rate of anal cancer among HIV-positive people in France has stabilized in the current era, according to French researchers it remains very high compared to that seen in HIV-negative people.
Montréal researcher François Coutlée, MD, has also been studying HPV and has reviewed studies comparing HPV-related disease in the pre-HAART and HAART eras. In a recent article in the journal Sexual Health, Dr. Coutlée wrote: "If HAART was truly protective against [HPV-related pre-cancers, new cases of anal cancer] would be decreasing, which is not what is being observed."
The French study uncovered a high risk of anal cancer among HIV-positive people, particularly in men and especially MSM. The risk of anal cancer in the current era among HIV-positive people compared to HIV-negative people was as follows:
Researchers in both France and the U.S. have sought explanations for the excessive risk of anal cancer seen in HIV-positive people. One possibility is that MSM and others at high risk for HIV infection may become infected with cancer-causing strains of HPV at an earlier age than HIV-negative people. This may allow HPV-infected cells more time to develop abnormally, thus a greater risk of developing pre-cancer and cancer.
In general, the immune system becomes less effective as people age and there is a suggestion that viral infections, particularly those caused by CMV (cytomegalovirus, a member of the herpes family of viruses), may prematurely age the immune system. Added to this is the burden of HIV infection, which is associated with hints of acceleration in the aging of the immune system. Being co-infected with different viruses may weaken the immune system's ability to contain and control the growth of pre-cancers and tumours.
Theories and evidence for accelerated aging of the immune system in the context of HIV infection are somewhat controversial and require further research.
In most high-income countries the threshold for starting ART is at least 350 cells. In cases where symptom-free HIV-positive people have co-existing health issues -- including conditions that affect major organs such as the brain, heart, liver and kidneys -- treatment may be recommended or encouraged at higher CD4+ count thresholds, even if a person has more than 500 cells. In such cases, treatment helps to strengthen the immune system and reduce HIV-related inflammation and the risk of damage to organ-systems caused by HIV and/or co-infections.
A key risk factor for anal cancer in the French study was having a low nadir CD4+ cell count. On average, 50% of HIV-positive participants who developed anal cancer had a nadir CD4+ count less than 95 cells.
The French researchers stated that if more HIV-positive people initiated ART at relatively high CD4+ counts, then fewer people would experience low nadir CD4+ cell counts and would therefore be at greatly reduced risk for the subsequent development of anal cancer.
Researchers in Québec have also found that a low nadir CD4+ count is associated with an increased risk for anal pre-cancer and cancer among HIV-positive men.
Here are some steps that might help reduce the future risk for HPV-related cancers, including anal cancer:
Starting ART before the CD4+ count falls to low levels helps to reduce damage to the immune system. A stronger immune system should be better able to fend off cancers.
There are two vaccines -- Cervarix and Gardasil -- that provide protection against two strains of HPV that are associated with cancer. One of these vaccines (Gardasil) also provides protection against ano-genital warts. Although the effectiveness of these vaccines was tested in HIV-negative people, researchers at the U.S. National Cancer Institute recently estimated that these vaccines could provide "substantial" protection against HPV-related pre-cancer and cancer particularly in HIV-positive people. Speak to your doctor about coverage for this vaccine in your region.
Reducing exposure to factors associated with cancer (such as tobacco smoke, excessive alcohol and injecting street drugs) is a good step. Another important step is getting help for the mental and emotional health conditions that often underpin some people's susceptibility to addictive behaviours and substance use.
This helps to protect people not only from HIV infection (and for HIV-positive people, new strains of the virus) but also from many sexually transmitted infections. Correct and consistent use of condoms offers some protection from (re)infection with HPV.
Anal cancer screening programs for HIV-positive people may be available in some larger cities. Often such programs are funded as part of research studies and may not be the standard of care. Speak to your doctor about the availability of this screening in your region.