OCCUPATION AND PROSTATE CANCER AGGRESSIVENESS

Long-haul truckers and men working in garden-supply shops might be more likely to have highly aggressive prostate cancer on diagnosis, according to a presentation at the 12th Annual International Conference on Frontiers in Cancer Prevention Research, held in National Harbor, Maryland.

Plausible explanations for the findings include the whole-body vibrations commonly experienced by truckers and the potential chemical exposure from indoor pesticide storage, lead author L. Joseph Su, MD, MPH, from the National Cancer Institute in Rockville, Maryland, told Medscape Medical News.

Dr. Su and colleagues reviewed the employment history of 2132 men with newly diagnosed disease in the North Carolina–Louisiana Prostate Cancer Project.

They found that truck drivers were almost 4 times more likely than educators to have highly aggressive disease (odds ratio [OR], 3.96; 95% confidence interval [CI], 1.02 - 15.46). For men who worked at a garden shop for 6 or more months, the risk was more than doubled (OR, 2.33; 95% CI, 1.21 - 4.45).

No association was found for men working in other jobs that were thought to be possibly risky, such as landscapers, animal caretakers, or exterminators.

Highly aggressive disease was defined as a Gleason score of at least 8, a prostate-specific antigen level above 20 ng/mL, or a Gleason score of at least 7 with stage T3/T4 disease.

"There are a small number of epidemiologic studies linking occupations that are involved in whole-body vibration and prostate cancer risk," Dr. Su explained. Other data have linked whole-body vibration with prostatitis (a known risk factor for prostate cancer) and elevated testosterone levels (a potential risk factor).

"We used educators as a comparison group because their potential exposure to known occupational hazards (other than stress) is minimal," Dr. Su added, noting that adjustments were made for age, body mass index, and other potential confounders.

It is important to realize that in this study, correlation does not imply causation, Richard Stevens, PhD, professor of cancer epidemiology at the University of Connecticut Health Center in Farmington, toldMedscape Medical News.

"This is a very strong and well-done study showing that men with aggressive prostate cancer are much more likely to have been truck drivers, but it doesn't show that truck drivers are at an increased risk for prostate cancer," he explained.

It could be that truck drivers are diagnosed at a later stage because their lifestyle limits physician access, Dr. Stevens noted. In addition, the use of truck driving as a surrogate end point for vibration could introduce some variability into the mix.

"It could also be possible that being a truck driver significantly increases the risk for very aggressive cancer among men already prone to prostate cancer," he said. "We just don't know. But that's okay — this is the first study of its kind, and maybe these are real leads."

Dr. Su concurred: "Unfortunately, our study, as others, used an epidemiologic study design based on self-reported occupational history — in this case, the longest-held job. It cannot offer causality, nor can it offer the exact mechanism for the association observed."

More Study Needed

Dr. Stevens said the findings can serve as a foundation for future research in a field that has investigators baffled.

"As cancer researchers, we are flailing around, trying to find a cause for prostate cancer, and these are new ideas. Their merit depends on whether the findings can be replicated in other studies," Dr. Stevens said.

In the interim, Dr. Su's group plans to re-examine the dataset for factors that, in addition to the whole-body vibration hypothesis, could contribute to the findings.

Diet, obesity, long periods of sitting, and lack of exercise could all play a role, Dr. Su conceded. No significant association has yet been uncovered between lower activity levels and prostate cancer aggressiveness.

The North Carolina–Louisiana Prostate Cancer Project is supported by a contract from the National Department of Defense. Dr. Su and Dr. Stevens have disclosed no relevant financial relationships.

12th Annual International Conference on Frontiers in Cancer Prevention Research: Abstract B63. Presented October 29, 2013.