title: Larger men have larger prostates: Detection bias in epidemiologic studies of obesity and prostate cancer risk.
abstract: 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.
authors.affiliation: Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, New York.
authors.forename: Andrew
authors.identifier: http://orcid.org/0000-0003-0211-7707
authors.initials: A
authors.lastname: Rundle
authors.affiliation: Department of Public Health Sciences, Henry Ford Health System, Detroit, Michigan.
authors.forename: Yun
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Public Health Sciences, Henry Ford Health System, Detroit, Michigan.
authors.forename: Sudha
authors.initials: S
authors.lastname: Sadasivan
authors.affiliation: Department of Pathology, Henry Ford Health System, Detroit, Michigan.
authors.forename: Dhananjay A
authors.initials: DA
authors.lastname: Chitale
authors.affiliation: Department of Pathology, Henry Ford Health System, Detroit, Michigan.
authors.forename: Nilesh S
authors.initials: NS
authors.lastname: Gupta
authors.affiliation: Environmental Health Sciences, Mailman School of Public Health, Columbia University, New York, New York.
authors.forename: Deliang
authors.initials: D
authors.lastname: Tang
authors.affiliation: Department of Public Health Sciences, Henry Ford Health System, Detroit, Michigan.
authors.forename: Benjamin A
authors.initials: BA
authors.lastname: Rybicki
mesh_terms: D015982:Bias; D015992:Body Mass Index; D049628:Body Size; D016021:Epidemiologic Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000175:diagnosis / Q000453:epidemiology; D009929:Organ Size; D011467:Prostate / Q000473:pathology*; D017430:Prostate-Specific Antigen / Q000032:analysis; D011471:Prostatic Neoplasms / Q000453:epidemiology / Q000473:pathology; D018570:Risk Assessment; D012307:Risk Factors; D013223:Statistics as Topic
chemical_list: D017430:Prostate-Specific Antigen
keywords: obesity; prostate cancer; prostate volume