People with AIDS are not developing most non-HIV-related cancers at a younger age than individuals in the general population, US investigators report in the October 5th edition of the Annals of Internal Medicine.
The investigators noted significant structural differences in the ages of those with AIDS and patients in the general population. Once adjustment was made for these differences, the investigators found that the age at which individuals with AIDS developed many non-HIV-related cancers was broadly comparable to that observed in the general population.
“Previous studies that reported younger ages at cancer diagnosis in persons with HIV/AIDS did not take into account that very few HIV-infected persons who are at risk of cancer have attained older age, when most cases of cancer develop”, comment the investigators, “this underlying age difference creates a bias when the ages of cancer diagnosis are compared between these population.”
To try and correct for this bias, the investigators adjusted the age profile of the general population.
Their study population involved 212,055 people enrolled in 15 US HIV cancer registries who were diagnosed with HIV between 1996 and 2007.
The age at which 26 non-AIDS-defining cancers developed in these patients was compared to that observed in the general population. In addition, the investigators compared the incidence of cancers between the two groups.
Most (76%) of the HIV-positive patients were male, 42% were black and their median age at the time of their diagnosis of AIDS was 38 years.
After the onset of AIDS, a total of 2540 patients were diagnosed with a non-AIDS-defining cancer. The most common were lung cancer (24%), anal cancer (11%) and Hodgkin lymphoma (9%).
The median age of the HIV-positive and control populations was broadly similar (40 vs. 35 years). However, only 1.5% of patients with AIDS were aged 65 and above compared to 12.5% of individuals in the general population.This difference was important because most cancers in the general population develop in individuals in individuals who are 65 and older.
Consistent with this different age profile, patients with AIDS were aged approximately 20 years younger at the time cancer developed than people in the general population.
However, after adjusting for structural differences in the ages of the two populations, there was no real difference in the age at cancer diagnosis between people with AIDS and patients in the general population.
Nevertheless, age differences persisted for three cancers. Individuals with AIDS developed two cancers at a younger age (anal cancer: 42 vs. 45, p < 0.001; lung cancer 50 vs. 54, p < 0.001). However, the age at which they developed Hodgin lymphoma was significantly older (42 vs. 40, p < 0.001).
Breast, colon and prostate cancer were more common in the general population than in patients with AIDS. Correction for structural differences in the age profiles of the two populations meant that there was no difference in the average age at which they developed these cancers.
Anal cancer, Hodgkin lymphoma and lung cancer (p < 0.001) were all more common in patients with AIDS than those in the general population. The investigators note that both anal cancer and Hodgkin lymphoma are linked to infections, and therefore suggest their higher incidence in people with AIDS could be explained by risk behaviour. As regards the higher incidence of lung cancer, the researchers suggest that this is likely to be due to longer duration of smoking and greater smoking intensity among patients with AIDS.
“When we did not account for underlying population age structures, we found that many types of cancer occurred at much younger ages in persons with AIDS”, write the investigators (52 vs. 72 years]”.
However, “these dramatic age differences are influenced by age differences in the population at risk” and largely disappeared when this was controlled for in the investigators’ analyses.
“Our results do not support including cancer as part of a general syndrome of premature aging in HIV-infected persons”, conclude the authors.
They therefore do not believe that more intensive cancer screening for many non-AIDS-defining cancers – such as prostate, colon, or breast cancer - is warranted in patients with HIV.
Although the authors of an accompanying editorial praise the study as “an important stepping stone in our path to clarifying a relationship of HIV with premature aging”, they are not entirely convinced by its findings and call for more research.
Shiels MS et al. Age at cancer diagnosis among persons with AIDS in the United States. Annals of Internal Medicine, 153: 452-60, 2010. (link to abstract)
Martin J et al. HIV and premature aging: a field still in its infancy. Annals of Internal Medicine, 153: 477-50, 2010.