Larger Men Have Larger Prostates: Detection Bias in Epidemiologic Studies of Obesity and Prostate Cancer Risk

Prostate. 2017 Jun;77(9):949-954. doi: 10.1002/pros.23350. Epub 2017 Mar 27.


Background: Obesity is associated with risk of aggressive prostate cancer (PCa), but not with over-all PCa risk. However, obese men have larger prostates which may lower biopsy accuracy and cause a systematic bias toward the null in epidemiologic studies of over-all risk.

Methods: Within a cohort of 6692 men followed-up after a biopsy or transurethral resection of the prostate (TURP) with benign findings, a nested case-control study was conducted of 495 prostate cancer cases and controls matched on age, race, follow-up duration, biopsy versus TURP, and procedure date. Data on body mass index and prostate volume at the time of the initial procedure were abstracted from medical records.

Results: Prior to consideration of differences in prostate volume, overweight (OR = 1.41; 95%CI 1.01, 1.97), and obese status (OR = 1.59; 95%CI 1.09, 2.33) at the time of the original benign biopsy or TURP were associated with PCa incidence during follow-up. Prostate volume did not significantly moderate the association between body-size and PCa, however it did act as an inverse confounder; adjustment for prostate volume increased the effect size for overweight by 22% (adjusted OR = 1.52; 95%CI 1.08, 2.14) and for obese status by 23% (adjusted OR = 1.77; 95%CI 1.20, 2.62). Larger prostate volume at the time of the original benign biopsy or TURP was inversely associated with PCa incidence during follow-up (OR = 0.92 per 10 cc difference in volume; 95%CI 0.88, 0.97). In analyses that stratified case-control pairs by tumor aggressiveness of the case, prostate volume acted as an inverse confounder in analyses of non-aggressive PCa but not in analyses of aggressive PCa.

Conclusions: In studies of obesity and PCa, differences in prostate volume cause a bias toward the null, particularly in analyses of non-aggressive PCa. A pervasive underestimation of the association between obesity and overall PCa risk may exist in the literature.

Keywords: obesity; prostate cancer; prostate volume.

MeSH terms

  • Bias
  • Body Mass Index
  • Body Size
  • Epidemiologic Studies
  • Humans
  • Male
  • Middle Aged
  • Obesity* / diagnosis
  • Obesity* / epidemiology
  • Organ Size
  • Prostate / pathology*
  • Prostate-Specific Antigen / analysis
  • Prostatic Neoplasms* / epidemiology
  • Prostatic Neoplasms* / pathology
  • Risk Assessment
  • Risk Factors
  • Statistics as Topic


  • Prostate-Specific Antigen