HIV-positive people had a higher rate of new anal cancer than HIV-negative people in a comparison involving thousands of people in the United States and Canada.1 HIV-positive gay and bisexual men had more than an 80 times higher anal cancer rate than HIV-negative people in this study.
Because strong antiretroviral combinations that HIV-positive people started taking in the 1990s greatly lowered the AIDS death rate, a growing proportion of people with HIV now die of cancer, especially cancers caused by infections. Anal cancer can be caused by human papillomavirus (HPV) infection in men and women. Like HIV, HPV can pass from one person to another during sex, so many people with HIV also have HPV. In the United States, 2700 women and 1500 men get HPV-related anal cancer every year.2
Previous large studies found that HIV-positive people have a 30 times higher anal cancer rate than the general population.3,4 But anal cancer incidence -- the rate of newly diagnosed cancers in a given period -- has varied widely from study to study. Gay and bisexual men have the highest anal cancer rates in these studies, but it's unclear how anal cancer rates differ in gay men, straight men, and women with HIV when compared with HIV-negative people.
To learn more about anal cancer rates in different groups of HIV-positive people, U.S. and Canadian researchers planned this new study.
The study involved HIV-positive men and women who were members of 10 U.S. and 3 Canadian HIV study groups from 1996 through 2007. A comparison group of HIV-negative men and women came from 3 of the 10 U.S. study groups. The analysis did not include anyone who already had anal cancer when they entered their study group.
Researchers counted the number of new anal cancers detected (anal cancer incidence) during the study period. The main goal of the study was to estimate anal cancer incidence in three HIV-positive groups: gay and bisexual men, "other men" who became infected with HIV during sex with women or when injecting drugs, and women.
The researchers used standard statistical methods to compare anal cancer incidence in these groups with incidence in HIV-negative men and women according to year (1996-1999, 2000-2003, and 2004-2007), age (in 5-year groups), and race or ethnicity. They also figured how cancer incidence changed in these groups through the three study periods (1996-1999, 2000-2003, and 2004-2007).
In addition, the research team analyzed anal cancer incidence in the HIV-positive groups by calculating standardized incidence ratios. This statistic compared anal cancer rates in the HIV-positive groups with rates in a nationwide U.S. database called SEER (for Surveillance, Epidemiology, and End Results). This analysis accounted for the potential impact of age and race or ethnicity on cancer rates. The researchers conducted this analysis because the HIVnegative group in the main comparison included people from only 3 of the 10 study groups -- and the research team wanted to make sure that comparison was accurate.
The study involved 18,855 HIV-positive gay or bisexual men (55% of the HIV group), 6492 other HIV-positive men (19% of the HIV group), and 8842 HIV-positive women (26% of the HIV group). The comparison group had 102,607 HIVnegative men and 11,653 HIV-negative women.
Median age was similar across all of these groups at about 38 years. Whites made up 63% of the gay/bisexual HIV group, while blacks made up 52% of the other HIV-positive men and 54% of HIV-positive women. Among HIV-positive women and other men with HIV, about 60% picked up HIV during sex.
Anal cancer incidence (the new diagnosis rate) per 100,000 person-years was 131 for HIV-positive gay/bisexual men, 46 for HIV-positive other men, 30 for HIV-positive women, and 2 for HIV-negative men. Anal cancer developed in no HIV-negative women during the study period. Compared with HIV-negative men, HIV-positive gay/bisexual men had an 80.3 times higher rate of new anal cancer and HIV-positive other men had a 26.7 times higher rate.
For HIV-positive gay/bisexual men, other men, and women, anal cancer incidence was lowest in 1996-1999, the first years of the combination antiretroviral therapy era (Figure 1). The new anal cancer rate rose sharply in 2000-2003 and remained at about that level in 2004-2007.
Figure 1. Rates at which anal cancer developed in HIV-positive people rose substantially from the first study period (1996-1999) to the second study period (2000-2003), then remained at about that level in the third study period (2004-2007). The new anal cancer rate was higher in HIV-positive gay or bisexual men than in other HIV-positive men or HIV-positive women.
Another analysis compared the new anal cancer rate in the three HIV-positive groups with the rate in a large U.S. national database (Table 1). This analysis showed much higher anal cancer rates in the HIV-positive groups than in the general population. The anal cancer rate difference between the HIVpositive groups and the general U.S. population was highest for gay or bisexual men.
|Table 1. New Anal Cancer Rates in Three HIV-Positive Groups Compared With the U.S. General Population*|
|Rate Compared With General Population*|
|Gay/Bisexual HIV+ Men||Other HIV+ Men||HIV+ Women|
* Rates are reported as standardized incidence ratios. A standardized incidence ratio of 73.9 in 1996-1999, for example, means that gay/bisexual had a 73.9 times higher rate of new anal cancer than the general population in those years.
† Rate was 0 in 1996-1999 because anal cancer developed in only 1 HIV-positive woman in those years and data on her were incomplete.
Finally, statistical analysis that figured in the impact of several cancer risk factors found a significant difference in risk of new anal cancer in the following groups:
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