December 17, 2008
HIV infection, because it weakens the immune system, is linked to an increased risk for the development of certain cancers, including the following:
This cancer risk arises in part because the various viruses that cause these cancers are sexually transmitted and commonly found in HIV positive people.
Highly active antiretroviral therapy (HAART) is widely available in most high-income countries. This therapy works by decreasing levels of HIV, allowing the immune system to begin repairing itself. However, the renewal of the immune system is only partial, despite years of using HAART. Because of this incomplete recovery, HAART users remain at heightened risk for cancer.
Among some people at risk for and who have HIV, the use of illicit drugs, such as the following, is relatively common:
Some of these drugs can weaken the immune system. Not surprisingly, American researchers who monitor the health of substance users with HIV infection have uncovered some troubling trends. Specifically, the use of amphetamine appears to be linked to the development of cancer of the immune system (lymphoma).
The American Multicenter AIDS Cohort (MACS) has been monitoring the health of men at risk for and who have HIV infection since the early 1980s. Researchers with MACS analysed their database looking at health information collected between 1984 and 2002.
They focused on 1,788 men who were HIV positive at the time they entered MACS and 461 men who were initially HIV negative but during the course of the study became HIV positive, for a total of 2,249 HIV positive men. At the time they entered the study the men had the following average profile:
On the whole, amphetamine users were relatively young, tended to smoke tobacco and engaged in unprotected sex from time to time.
During the study, 171 cases of lymphoma (specifically non-Hodgkin's lymphoma) occurred.
Men who used amphetamine frequently (once weekly or more) were nearly five times more likely to develop lymphoma than men who did not use amphetamine as often. This link was statistically significant; that is, not likely due to chance alone. Also, the study team found a statistical link between the use of amphetamine three years before the development of lymphoma.
Exposure to cocaine, marijuana and other illicit drugs were not linked to the development of lymphoma.
Two previous studies, both done in the 1990s, did not find a link between amphetamine exposure and cancer. In part, this may be due to differences in substance-using behaviour of the people in those studies; amphetamine use was relatively lower when compared to the present, longer study.
One other study found a link between amphetamine exposure and the development of lymphoma. But in that study, amphetamines were mostly used under medically supervised conditions as part of a weight-loss program. Because obesity is a risk factor for the development of lymphoma it is not clear if amphetamines did indeed play a role in the rise in cancers seen in that study.
Results from laboratory studies with cells, animals and amphetamines suggest that this drug weakens the immune system. Short-term studies in people who used drugs chemically related to amphetamine, such as ecstasy, have found reduced levels of CD4+ cells and other assessments of weakened immunity.
Prior research on HIV positive people at heightened risk for lymphoma have found higher-than-normal levels of certain immune system signals at least three years before symptoms of lymphoma appeared. This is interesting in light of the present study's finding that links amphetamine use three years prior to the subsequent development of lymphoma. This finding supports this idea:
Use of amphetamines and related compounds (crystal meth, ecstasy) has previously been linked to episodes of depressive illness and changes in personality. Moreover, use of methamphetamine is highly addictive and can cause deep and lasting neurological damage. Now, the MACS research adds yet another reason to avoid the use of these substances. As a result of their findings, the American researchers call for further study on the immunologic and cancer-causing potential of amphetamine on both HIV negative and HIV positive people.