• Occupational and Environmental Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Department of Health and Human Services, Rockville, MD, USA.
• Department of Epidemiology and Public Health, University of Maryland School of Medicine, Baltimore, MD, USA.

BACKGROUND: Though obesity, measured by body mass index (BMI), is an established risk factor for several cancer sites, there is conflicting evidence on whether obesity increases prostate cancer risk or mortality, and if it does, whether it increases risk directly or indirectly by affecting prostate cancer screening efficacy.

METHODS: We examined associations between BMI and prostate cancer screening outcomes, incidence, and mortality in men randomized to the intervention arm of the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial (n = 36,756) between 1993-2001. Participants received annual screening with the prostate specific antigen (PSA) test and digital rectal exam (DRE). Associations between baseline BMI and screening outcomes were assessed via multinomial logistic regression, and associations with prostate cancer incidence and mortality were assessed via Cox proportional hazards regression.

RESULTS: Individuals with higher BMI were less likely to screen positive via the PSA test and/or DRE and more likely to have an inadequate screen (all p-trend < 0.01). Higher BMI was inversely associated with prostate cancer incidence (hazard ratio [95% confidence interval] per 5 kg/m2 BMI increase: 0.94[0.91-0.97]), including incidence of early-stage (0.94[0.90-0.97]) and advanced-stage (0.91[0.82-1.02]) disease, but positively associated with prostate cancer mortality (1.21[1.06-1.37]). The association with mortality was not modified by screening outcome (p-interaction = 0.13).

CONCLUSIONS: Within this screened population, individuals with higher BMI had lower risk of prostate cancer diagnosis but higher risk of prostate cancer mortality. As higher BMI was not positively associated with advanced-stage prostate cancer risk, the increased mortality is unlikely to be due to delayed prostate cancer detection.