Researchers behind a new study published in the International Journal of Cancer were surprised when their analysis showed that men with asthma appear to have a lower risk of developing lethal prostate cancer. Previous studies have suggested the kind of inflammation associated with asthma is also associated with prostate cancer.
However, the authors, led by Elizabeth A. Platz, a professor of epidemiology at Johns Hopkins Bloomberg School of Public Health in Baltimore, MD, caution that their findings can only show a link - they cannot prove cause and effect.
For their study, the team analyzed data from questionnaire responses and medical records belonging to 47,880 men aged 40-75 taking part in the Health Professional Follow-Up Study (HPFS) run by the Harvard T.H. Chan School of Public Health.
None of the men had been diagnosed with cancer when they joined HPFS in 1986, and they were followed until 2012. The participants filled in questionnaires every two years, so the data set contained ongoing information about their background, demographics, use of medications, medical history, and lifestyle.
If participants mentioned being diagnosed with prostate cancer, the researchers consulted their medical records and pathology reports.
The analysis showed that having a history of asthma was linked to a 29% lower likelihood of being diagnosed with metastatic prostate cancer (cancer that has spread from the original tumor) or dying of the disease.
Overall, the analysis revealed that men with asthma were 36% less likely to die of prostate cancer. Even when they took into account factors such as whether the men were taking asthma medication or whether the condition was diagnosed early or later in life, the researchers found the association was the same.
Men with hay fever were more likely to be diagnosed with lethal prostate cancer
Prof. Platz warns that their study cannot prove that having asthma reduces the risk of lethal prostate cancer - being an observational study, it could only explore associations between factors and say how strong they were.
The team also found a link between lethal prostate cancer and hay fever, but in this case the link was weaker and in the other direction. Men with hay fever were 10-12% more likely to be diagnosed with lethal prostate cancer and to die of it.
The researchers undertook the study because of previous research in mice that had shown immune cells that infiltrate prostate tumors trigger an immune response known as Th2 inflammation.
Their thinking was they would find a higher rate of lethal prostate cancer in men with asthma because asthma is often considered to be a disease of chronic inflammation and Th2 inflammation in particular. Cancer is also thought of as a disease involving Th2 inflammation.
Instead, their analysis showed the opposite - men with asthma appear to have a relatively lower risk of lethal prostate cancer.
Researchers now want to investigate immune cells in the prostate to explain the findings
Prof. Platz says their study is the first to analyze the link between asthma and prostate cancer - with a focus on lethal prostate cancer - in such a large group.
Speculating on the reasons behind the surprising findings, the authors suggest perhaps the Th2 inflammation that drives asthma is not the same as the Th2 inflammation that drives cancer. Alternatively, people with asthma may have higher levels of other immune cells that might attack cancer cells.
Prof. Platz says they are going to carry on with their work in the laboratory and try to find out more about the immune cells in the prostate. She explains:
"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."
Funds for the study came from the National Cancer Institute and the National Heart, Lung and Blood Institute.
Meanwhile, Medical News Today recently reported another surprising discovery of a previously unidentified potential biomarker for aggressive prostate cancer.
Writing in the journal Oncogene, a team from the University of Michigan suggests that a protein called Runx2 whose function is to produce bone may also control the growth of prostate cells. If this proves to be so, it could be a potential biomarker to distinguish between fast- and slow-growing tumors.