Men with a history of asthma appear less likely to develop lethal prostate cancer, though it’s not clear why.
Men with an asthma history were 29 percent less likely than non-asthmatics to be either diagnosed with prostate cancer that spread elsewhere in the body or to die of the disease. Looking at fatalities alone, asthmatic men were 36 percent less likely to die of prostate cancer.
But this doesn’t mean that asthma protects men from prostate cancer.
“We don’t know yet whether the association we see in this observational study is a case of cause-and-effect,” says Elizabeth A. Platz, an epidemiologist at Johns Hopkins University Bloomberg School of Public Health and Johns Hopkins Kimmel Cancer Center.
The findings are particularly surprising because some studies have suggested that prostate cancer is linked to the kind of inflammation associated with asthma, which itself is a chronic inflammatory condition, Platz says.
For the study, published in International Journal of Cancer, researchers also analyzed links between a history of hay fever and lethal prostate cancer and found a smaller but opposite association: men with hay fever were 10 to 12 percent more likely to develop lethal or fatal prostate cancer.
The 47,880 men, aged 40 to 75, were in Harvard University’s Health Professionals Follow-Up Study from 1986 through 2012. They completed a questionnaire every two years, reporting on demographic information, medical history, medication use, and lifestyle factors.
Researchers evaluated medical records and pathology reports on those diagnosed with prostate cancer during the study. About 9 percent reported a history of asthma, while 25 percent had been diagnosed with hay fever. There were 798 confirmed lethal prostate cancer cases in the group.
Several reasons why
The researchers then began looking at a possible connection between asthma and prostate cancer based on work in mice showing that the immune cells that infiltrate prostate tumors produce an immune response known as Th2 inflammation.
“Asthma is often considered to be a disease of chronic inflammation, particularly Th2 inflammation,” says Charles Drake, co-director of the Prostate Cancer Multidisciplinary Clinic at the Kimmel Cancer Center. “And cancer is often thought of as mediated by Th2 inflammation. So what we expected was that asthmatics would have a higher incidence of prostate cancer.”
Instead, the new analysis “showed the exact opposite, that men with asthma had a relatively lower risk of prostate cancer,” Drake says.
There are several possible reasons why asthma might not be linked to a higher risk of lethal prostate cancer.
“It’s possible that the Th2 inflammation that drives asthma is not the same as the Th2 inflammation that drives cancer,” he says. It may also be that asthmatics have higher levels of other immune cells that might attack tumor cells.
The researchers will next “go back into the lab and try to characterize the nature of the immune cells present in the prostate,” Platz says. “We want to see what it is about a particular immune profile or immune environment that might be related to prostate cancer, especially aggressive prostate cancer.”
Researchers from Harvard University, Washington University in St. Louis, University of California, San Francisco, contributed to the study. The National Cancer Institute and the National Heart, Lung and Blood Institute funded the work.
Source: Johns Hopkins University