The challenge with this kind of research is that it is trying to do something that requires a controlled experiment. It is very hard to prove with this kind of research that obesity itself results in an increased risk of prostate cancer.
The questions that remain are: Is there something that leads to obesity that also leads to prostate cancer, or does the obesity lead to prostate cancer? Obesity may be associated with other behaviors that increase the risk of prostate cancer, in which case the obesity is not the key variable.
There are many beliefs that the western diet is associated with a higher risk for prostate cancer independent of whether people are obese or not. All of this is hard to control for. Other issues are that obesity can be associated with changes in hormone levels and hormone levels may be associated with prostate cancer development.
Therefore, there is a certain amount of skepticism that we have to bring to epidemiological studies. Many just look at a population and a particular characteristic in the population, and then correlate it with an outcome. We can easily mistake that for causality. We saw that very clearly with the WHI; that all the epidemiological data seemed to indicate that if you gave women HT it would lower their risk for cardiovascular disease. In fact, there was a time in the 90s when medical students were being taught that all postmenopausal women should be put on HT.
Following a proper trial where researchers randomized women on HT vs. no HT, some studies showed a higher risk for cardiovascular disease. This was the opposite of what some people expected.
There have been multiple reminders historically in medicine that this kind of epidemiological data can generate questions or hypotheses, but it is not very good for answering questions.
A more compelling demonstration that there was some kind of causal link between obesity and prostate cancer would be to conduct a study examining weight loss in men who change their behavior and exercise more frequently; eating healthier diets, and then assessing their risk for prostate cancer.
Overall, it was an interesting study. There’s been a lot of interest in whether obesity is associated with a risk for cancer.
Timothy Gilligan, MD
Medical oncologist specializing in cancers of the testicles, bladder, prostate and kidneys
Department of solid tumor oncology
Cleveland Clinic Taussig Cancer Institute
Disclosures: Gilligan reports no relevant financial disclosures.