Dr. June Chan is a Professor in the Departments of Epidemiology and Biostatistics and Urology at the University of California, San Francisco.
Her research focuses on how diet, exercise, and lifestyle factors contribute to prostate cancer aggressiveness, progression, and death.
Prostatepedia spoke with her about the impact of diet and lifestyle on prostate cancer.
What do we currently know about the relationship between diet, lifestyle, and prostate cancer?
Dr. Chan: We have observed that there are some relationships between diet and exercise and the risk of clinically relevant prostate cancer. As our studies evolved—and the field evolved alongside the development of PSA screening in the United States—it became important to define and focus on clinically relevant prostate cancer as an outcome.
Back in the early to mid-1990s when some of our first studies came out, we were just looking at specific dietary factors and the risk of overall development of prostate cancer. With PSA screening came the understanding that there are indolent tumors and overdiagnosis; we needed to adjust to that in the field.
Part of my work as a postdoctoral fellow was to collect detailed data in large cohort studies so we could classify men in a more clinically meaningful way. We collected details on stage, grade, and subsequent PSA values so that we could try to distinguish more indolent tumors from more aggressive tumors.
Once we started to do that, it became more interesting because we really started to refine our questioning. The question isn’t just, “Is vegetable intake associated with overall risk?” The question becomes: “Is vegetable intake associated with the risk of having bad prostate cancer? A cancer that will do harm.” As studies have matured, we’ve focused on the risk of developing metastases and prostate cancer-specific mortality.
The field had to change as we started to understand the biology of prostate cancer better. Some of that early observational data that came from us looking at total prostate cancer risk needed to be looked at again. That is the stage we’re in now. We look at those questions differently now that we have more clinically relevant outcomes with more time.
What do we know about the impact diet and lifestyle have on the risk of developing prostate cancer? What do we know about the impact diet and lifestyle have on progression? About the risk of developing aggressive versus low-risk disease?
Dr. Chan: I’ll focus on what we know about clinically relevant cancer or, at least, some of the findings that have persisted over time.
The first thing, which is not discussed as much, is that smoking is potentially related to the risk of fatal prostate cancer. Some of the earliest data come from autopsy studies. They looked at people who had not necessarily been diagnosed with prostate cancer but had died for some other reason. They were able to correlate smoking history with a worse-looking grade and worse- looking features of prostate cancer.
Dr. Stacy Kenfield published a paper looking at the risk of fatal prostate cancer and smoking history. Her work showed that smoking has a broad effect —not just on respiratory cancers. Smoking elevates your risk of other cancers as well.
Some of our work indicates that exercise may be important for deterring the risk of having recurrent or fatal prostate cancer. The story started with two reports that we put out in 2011. Dr. Kenfield led one team and Dr. Erin Van Blarigan led the other. (I was mentoring both researchers.) We had the opportunity to ask about exercise and prostate cancer survivorship in two distinct populations. The results were somewhat complementary.
In one study, it appeared that vigorous physical activity was associated with a benefit or reduction in the risk of metastatic fatal prostate cancer among men diagnosed with localized disease.
The other study had a shorter follow-up, so we weren’t able to look at metastasis and death, but we did look at a combined outcome of recurrence, metastasis, and death —or the initiation of secondary treatment after primary therapy in prostate cancer survivors.
While there was a trend toward a benefit for physical activity, what was particularly interesting was that we saw a benefit from brisk walking versus slower walking pace. It suggested that there was something specific about aerobic exercise, or cardiopulmonary exercise, that offered a benefit. We’ve been pursuing that in other studies.
What do you mean by benefit?
Dr. Chan: In one study, there was a reduced risk of prostate cancer recurrence. In the other study, there was a reduced risk of prostate cancer death.