A large survey analysing rates of cancer diagnoses in the United States has confirmed that the number of new cases of anal cancer has increased since the start of the HIV epidemic. The survey’s findings were presented in the 1st December edition of The Journal of Acquired Immune Deficiency Syndromes.
Although the survey did not collect information on HIV status, it found elevated rates of anal cancer in the groups most heavily affected by HIV in the United States. This leads the investigators to recommend wider implementation of anal cancer screening programmes for the groups at greatest risk, particularly young men.
Anal cancer is caused by infection with certain strains of the human papilloma virus, the virus that causes warts. Unlike other types of cancer, the number of new cases of anal cancer seems to be increasing among HIV-positive patients, despite the introduction of powerful antiretroviral drug combinations. This may be due to a combination of incomplete immune system recovery allowing persistent infection with the wart virus, and the drugs extending the lifespan of HIV-positive patients.
The Surveillance, Epidemiology and End Results (SEER) programme is a register of the rates of new cases of cancer that collects data from around 14% of the United States population. Investigators from Memorial Sloan-Kettering Cancer Center in New York analysed the rates of new cases of anal cancer recorded in the register between 1973 and 2001.
The number of anal cancer cases increased between the ‘pre-HIV era’ (1973 to 1981) and the ‘HIV era’ (1982 to 1995), from 0.6 to 0.8 per 100,000 people. It increased again in the ‘highly active antiretroviral therapy (HAART) era’ (1996 to 2001), to 1.0 per 100,000 people.
Despite this trend, the investigators found that survival rates increased across the period analysed. Five-year survival was 63% in the pre-HIV era, 66% in the HIV era and 72% in the HAART era.
Rates of anal cancer were higher in women than in men across the period analysed. However, the proportion of cases occurring in men rose from 38% in the pre-HIV era, to 45% in the HAART era. In both sexes, the greatest increase in new cases occurred among 35- to 54-year-olds.
“Despite changes in HIV epidemiology and treatment associated with a stable or decreased incidence of certain HIV-associated malignancies, the incidence of [anal cancer] increased,” conclude the investigators.
“Early mortality among HIV-infected persons before the HAART era may have obscured increasing rates of [anal cancer] or its precursors. This may partially explain the marked increase of [anal cancer] between the HIV and HAART eras,” they continue.
Men were more likely than women to be diagnosed with early-stage anal cancer and to receive radiation therapy. In contrast, women were more likely to be diagnosed following the development of secondary tumours elsewhere in the body and to receive treatment with surgery.
“Since the introduction of HAART, the incidence of [anal cancer] has risen, particularly among men and younger individuals, the groups most affected by HIV,” the researchers write. “Given this increase, further studies are needed in high-risk populations to evaluate the best methods for prevention, early detection and treatment.”
This study was limited by its lack of information on HIV status and cancer treatment other than radiotherapy, as well as only five years’ follow-up since the introduction of HAART. However, it reinforces the data collected from cohorts of HIV-positive patients, and emphasises the effects that the HIV epidemic is having on the rates of cancer in the general United States population.
Chiao EY et al. A population-based analysis of temporal trends in the incidence of squamous anal canal cancer in relation to the HIV epidemic. J Acquir Immune Defic Syndr 40: 451-455, 2005.