Anal cancer incidence rates increased in antiretroviral era

Rates increased for men and women

Investigators compared United States surveillance data for cancer in the pre-HIV era, HIV era, and antiretroviral treatment era and found that squamous cell carcinoma of the anal canal incidence rates increased significantly in the latter era.1

"We took advantage of this public access data and tried to look at trends in anal cancer incidence," says Elizabeth Chiao, MD, MPH, an instructor at Baylor College of Medicine in Houston, TX.

"We're not the first group to have done that," Chiao says. "A lot of groups have looked at anal cancer incidence and have reported that it has increased in the last three decades or so," Chiao says. "So we broke it up with time cohorts that responded with basic epidemiologic trends in HIV epidemic."

The time cohorts were from 1973 to 1981, the pre-HIV era; from 1982 to 1995, the HIV era, and from 1996 to 2001, the era of highly-active antiretroviral drugs (HAART), Chiao explains.

"Truthfully, HAART was introduced in mid-1995, so these are rough estimates," Chiao notes.

The study found that the anal cancer incidence per 100,000 population increased from 0.6 per 100,000 population in the HIV era to 1.2 per 100,000 in the HAART era, Chiao says.

The incidence of anal cancer increase was most notable among men in the 35 to 54 age range, although there also was an increase in anal cancer incidence among women between the HIV era and HAART era, Chiao adds.

Since the surveillance data came from a National Cancer Institute (NCI) program called Surveillance, Epidemiology, and End Results, and it did not include HIV information, there are other possible explanations for the results, Chiao notes.

"Non-HIV infected men could be having sex with men, and this could explain it, but it's a little odd how it would follow trends of the HIV epidemic," Chiao says.

Also, it is known that people with HIV disease are at a much higher risk for anal cancer than people who not infected with HIV, Chiao says.

"There have been studies that have looked at anal cancer incidence in an HIV-infected population, and they estimate that whereas in the general U.S. population the incidence is possibly one per 100,000 or so, a relatively rare cancer, in the HIV population the incidence is 49 to 144 per 100,000 person years," Chiao says.

One theory explaining why anal cancer incidence increased in the HAART era is the hypothesis that partial immune reconstitution from HAART leads to longer life from HIV, but human papillomavirus (HPV) infection persists, Chiao explains.

"Even though HAART improves survival, your risk of HPV infection and persistent HPV infection and the ability to control those infections is still not quite normal, so you're at higher risk for prolonged HPV infection and dysplasia," Chiao says. "There could be an element that your own immune system is not effectively controlling it or that you're continually being exposed with unprotected intercourse."

Also, HIV-infected women have a more difficult time controlling HPV infection than do women who are not HIV infected, Chiao says.

Traditionally, anal cancer has been a cancer of women with a ratio of 1.6 women to 1 man in the pre-HIV era of people who have the cancer, Chiao says.

"Now the ratio is 1.2 women to 1 man, so HIV may be changing the epidemiology of anal cancer," she says.

The main issue for HIV clinicians to consider is whether or not HPV and anal cancer screening should be pursued actively in HIV infected patients, Chiao says.

There are a number of similarities between anal cancer and cervical cancer, which are both HPV related and preceded by changes in the squamous cells in the canal, Chiao notes.

Since screening for cervical cancer has been very successful in reducing the incidence of cervical cancer, the question is whether screening for anal cancer among HIV-infected men might also reduce the risk of anal cancer in that population, she adds.

Cost effectiveness modeling has shown that such screening would be cost effective, but the nation's medical community still questions whether such screening is feasible, Chiao says.

"Even if an individual clinic doesn't have the resources to do the anal cancer screening, at least they should use an external anal exam to look for lesions or evidence of HPV infection," Chiao says. "And at least once a year they should ask patients whether they've had symptoms of change, such as bleeding or a sensation of mass."

Reference:

  1. Chiao EY, Krown SE, Stier EA, Schrag, D. A population-based analysis of temporal trends in the incidence of squamous anal cancer in relation to the HIV epidemic. JAIDS. 2005;40(4):451-455.