In 2012 a massive observational study in Denmark compared nearly 19,000 people who had used statins to 277,000 people who had not used these drugs. Participants were HIV negative. Scientists found that participants who used statins were at a reduced risk for dying from complications caused by a range of cancers. Due to the study's observational design, researchers cannot prove that taking statins was linked to a reduced risk for cancer. It is possible that there were factors -- smoking tobacco, the size of tumours, the response to anti-cancer therapy -- that researchers did not take into account when analysing the data. Such factors could have inadvertently biased their conclusions.
Still, the Danish findings are interesting but at a minimum require confirmation from other large databases in other countries.
Previous studies suggest that HIV-positive people who use statins may be at reduced risk for HIV-related cancers, including non-Hodgkin's lymphoma.
Now researchers in Milan, Italy, have scoured the medical records of HIV-positive ART users to investigate the potential anti-cancer effect of statins. The researchers found that among about 5,357 participants, 740 people (14%) had a history of using statins. Among these statin users, 12 cases of cancers (2%) occurred vs. 363 cases of cancer (8%) among participants who did not use statins. Researchers estimated that statins helped to reduce the risk of cancer by about 55%. The cancers were those known to occur among some HIV-positive people, including lymphoma, Kaposi's sarcoma (KS) and cervical cancer.
Researchers at the San Raffaele Scientific Institute and associated hospital reviewed data collected from participants between January 1991 and October 2012. Cancer diagnoses were confirmed by a report from a pathologist who examined tumours.
Over the study period, researchers found 375 participants who developed cancer. The cancer cases were distributed as follows:
Twelve cancers (2%) occurred among statin users. All 12 cancers were unrelated to HIV.
A total of 363 cancers (8%) occurred among non-statin users, distributed as follows:
This difference in the number of cases between statin and non-statin users was statistically significant; that is, not likely due to chance alone.
The most commonly used statin was rosuvastatin (Crestor) 10 mg/day, followed by pravastatin 20 mg/day.
Overall, most participants began using statins about 11 years after their HIV diagnosis.
Researchers stated that statin users were "older, more frequently smokers [were overweight and entered the study with higher-than-normal blood pressure, cholesterol, triglyceride and blood sugar levels]." Thus, initially statin users had many risk factors for cardiovascular disease.
They also found that statin users tended to have higher pre-ART CD4+ cell counts and were less likely to be co-infected with hepatitis C virus than non-statin users.
This Italian study is also observational in design. Drawing robust conclusions from such studies is fraught with risk because of a problem called confounding. That is, researchers can never entirely rule out the presence of unmeasured factors that could potentially bias their results. Indeed the research team made the following statement:
"It is possible ... that statin users had a more favourable HIV status [such as higher pre-ART CD4+ counts] and different health behaviours that could lead to differences in cancer risk over time than [participants] who were not prescribed statins."
Researchers in the U.S. and France have commented on the Italian research in an editorial in the journal AIDS:
"It is possible (likely even) that statin users were more frequent visitors to [the study] clinic and therefore more likely to have controlled and suppressed [HIV viral load] and higher CD4+ cell counts over time. These factors would have decreased statin users' risk for [cancer]."
Analyses of observational studies are relatively easier, faster and cheaper than prospective, large randomized clinical trials. These days there are many demands for research dollars. However, due to low or stagnant economic growth and austerity policies in high-income countries, funds for scientific research are not increasing on a grand scale, and in some countries are even decreasing. Unless massive amounts of money are made available for scientific research, cheaper methods of attempting to answer research questions will become more common, even if such methods may not yield firm answers. As a result, some research and clinical issues may be plagued by lingering uncertainty.
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