Studies suggest that rates of anal cancer are increasing in both HIV-negative and HIV-positive people. Researchers in Toronto have reviewed data on anal cancer and suggested that rates of this cancer among HIV-positive men are similar to rates of cervical cancer among HIV-negative women before the routine use of Pap tests.
Anal cancer has similar features to cervical cancer, including the following:
- both cancers are associated with HPV (human papillomavirus) infection
- both cancers arise from pre-cancerous cells that have a similar appearance under the microscope
- pre-cancerous cervical growths can be detected with Pap smears and colposcopy (in women) and pre-cancerous anal growths by high-resolution anoscopy in men
The best way to detect abnormal and pre-cancerous cells in the anus is unclear. So a team of researchers conducted a study comparing three different assessments of pre-cancerous cells in the anuses of HIV-positive men. Their findings suggest that high-resolution anoscopy is the best method for finding pre-cancerous cells in the anus.
Researchers in Toronto recruited participants between 2001 and 2005. All participants were HIV-positive men who had a history of receptive anal intercourse. None had a history of anal cancer.
On entering the study, all participants underwent the following tests and procedures:
- anal Pap smears
- HPV testing
- high-resolution anoscopy (HRA)
In cases where pre-cancerous growths were detected, they were removed and participants returned to the study site for additional assessments.
The average profile of the 401 participants was as follows:
- age – 41 years
- age at first anal sex – 18 years
- duration of HIV infection – 14 years
- 31% had an AIDS-related illness in the past
- 76% were taking anti-HIV therapy
- 41% had a viral load less than 50 copies/ml in the blood
- 50% had a CD4+ count of 400 or more cells
- 92% had at least one gastrointestinal symptom within the past year – diarrhea, constipation, anal bleeding, anal pain and anal discharge
Researchers found that 24% of men had highly abnormal growths in their anus. These growths were classified as anal intraepithelial neoplasia (AIN 2+). Such growths are “mostly likely to lead to anal cancer,” the study team stated.
When these types of pre-cancerous growths were found, they were treated. This likely prevented the development of anal cancer. No cases of anal cancer were detected in the study.
The research team found that Pap tests were not good at detecting highly abnormal anal cells; Pap tests found them in only 12% of participants.
Nearly 90% of participants had cancer-causing types of HPV detected, most commonly HPV 16 (38%) and HPV 18 (20%). However, other cancer-causing types of HPV were also found, including these:
- HPV 53 in 20% of men
- HPV 52 in 18% of men
- HPV 31 in 16% of men
- HPV 33 in 15% of men
- HPV 56 in 12% of men
- HPV 68 in 12% of men
Since many participants denied recent sexual activity, the study team thinks that these high-risk HPV types represent long-standing infections. Persistent infection with these types of HPV likely increases the risk of pre-cancerous growths and anal cancer.
Weighing the evidence
The Toronto team stated: “Although there are no randomized controlled trials to support screening to prevent cervical cancer, [observational] studies have shown that cervical Pap testing and colposcopy with treatment of abnormalities has been associated with a marked reduction in cervical cancer.”
“Since HIV-positive men in this and other studies have a high rate of abnormal cells in the anus, given the strong parallels with cervical cancer, it would seem intuitive that detection and removal of these high-grade anal lesions (AIN 2+), particularly in HIV-infected men who have sex with men (MSM), might reduce anal cancer rates even though this is unproven.”
The research team notes that its findings will be useful when assessing the need for early anal cancer screening programs in HIV-positive MSM.
—Sean R. Hosein
- Crum-Cianflone NF, Hullsiek KH, Marconi VC, et al. Anal cancers among HIV-infected persons: HAART is not slowing rising incidence. AIDS. 2010 Feb 20;24(4):535-43.
- Salit IE, Lytwyn A, Raboud J, et al. The role of cytology (Pap tests) and human papillomavirus testing in anal cancer screening. AIDS. 2010; in press.