Anal cancer is a bad disease to get. In the general population, it is a rare cancer, found in about 1 per million people every year in the United States. But studies have shown that people in the groups referred to above are at higher risk. Among HIV-seropositive men with a history of receptive anal intercourse, the risk may be about 1 in a thousand men per year (no one really knows for sure). The risk is about a third of that for HIV-seronegative men with a history of receptive anal intercourse. Among HIV-seropositive women the risk is probably about 1 in 10,000 women per year. Again, no one really knows for sure.
These numbers indicate that on an individual basis, the risk of getting anal cancer is very low. Despite that, several thousand people die every year of anal cancer in the general population, and a high proportion of these are men with a history of anal intercourse, whether HIV-positive or HIV-negative. In the past, anal cancer usually occurred in people over the age of 60 years. In the last few decades or so, though, that has changed, particularly among HIV-seropositive men and women, in whom the average age of diagnosis is now in the 40's.
One of the major unanswered questions about anal cancer is whether HIV-seropositive men and women on highly active antiretroviral therapy (HAART) will be at lower risk of anal cancer due to HAART or higher risk. HAART has lowered the risk of several other types of cancer such as Kaposi's sarcoma so it would be logical to think the same may be true of anal cancer. On the other hand, since AIN2/3 can take many years to progress to cancer, it is possible that the increased survival time brought about by HAART may also give people the time to develop anal cancer of their AIN2/3 is not treated. The answer is not yet in, but early data suggest that if anything the risk of anal cancer will stay the same or continue to rise among people on HAART rather than drop.
The good news about anal cancer is that it is usually treated successfully if caught early. Most people will survive it. The bad news is that the recommended treatment for anal cancer - a combination of chemotherapy and radiation therapy- causes lots of side effects that can last for years. These can include severe anal pain (proctitis). For this reason, many experts believe that it is better to seek and treat AIN2/3 to prevent anal cancer since the treatment can be simple, even though in most cases the AIN2/3 would not have progressed to cancer even if left untreated. The problem is that clinicians have no way to distinguish the AIN2/3 that will progress from the ones that won't.
See the Anal Cancer section for a complete discussion of this topic.