Researchers at UT Southwestern Medical Center have found that non-AIDS-defining malignancies such as anal and lung cancer have become more prevalent among HIV-infected patients than non-HIV patients since the introduction of anti-retroviral therapies in the mid-1990s.
AIDS patients with suppressed immune systems are at higher risk for so-called AIDS-defining malignancies - cancers such as non-Hodgkin's lymphoma, Kaposi's sarcoma and cervical carcinoma. Some researchers have speculated, however, that HIV patients are diagnosed with more non-AIDS-defining malignancies simply because anti-retroviral drugs now used enable them to live longer, but the results of the UT Southwestern study suggest that other factors may be at work.
The researchers, using data from more than 100,000 patient records in the U.S. Veterans Affairs Healthcare System, found that when the statistics were adjusted for gender, race/ethnicity and age, HIV-infected patients were 60 percent more likely to have anal, lung, Hodgkin's, melanoma or liver cancer than patients without HIV. The rate of prostate cancer was similar between the two groups, according to the report.
"It's a genuine increase in the incidence of these cancers," said Dr. Roger Bedimo, assistant professor of internal medicine at UT Southwestern and lead author of a study appearing online and in the October edition of the Journal of Acquired Immune Deficiency Syndromes. "The increase is more visible because these patients are living longer, but our findings suggest that the increased number of non-AIDS-defining malignancies is not simply the result of their longer lives."
For the study, researchers compared the rates of non-AIDS-defining malignancies between patients with and without HIV who received care at a VA system facility between 1997 and 2004. For each HIV-positive patient, researchers identified at least two HIV-negative patients who received care the same year and matched them on age, sex, race and geographic location. The final study population included 33,420 HIV-infected patients and 66,840 non-infected patients.
The non-AIDS-defining malignancies included all forms of cancer except skin, lymphoma, cervical carcinoma, Kaposi's sarcoma and ill-defined cancers. Dr. Bedimo said the researchers examined anal, lung, melanoma, prostate, Hodgkin's and liver cancers - all non-AIDS-defining - individually.
Dr. Bedimo, chief of infectious disease at the Veterans Affairs North Texas Health Care System, said it's unclear exactly why non-AIDS-defining malignancies are more common in HIV patients than the general population. One controversial theory, he said, is that the anti-retroviral therapy itself might increase the risk of those cancers in HIV patients.
"The second hypothesis is that HIV-infected patients somehow, either by their lifestyle or other circumstances, are more subject to the traditional risk factors than non-HIV patients," he said. "The third hypothesis is that HIV or another undetected virus increases a patient's risk for developing cancer intrinsically."
Dr. Bedimo said that one major limitation of the study is the overrepresentation of males in the study. Males account for about 98 percent of the study population.
The next step is for researchers to examine other measures of immune function in patients with and without cancer.
"The hallmark of chronic HIV is a decline in CD4 T-cells, but we also know that HIV does a lot more to your immune system than just decrease the number of these cells," Dr. Bedimo said. "It's very possible that it is an immune dysfunction that impairs the cancer immune surveillance in patients even after their CD4 counts have increased."
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