title: Age-related prevalence of anal cancer precursors in homosexual men: the EXPLORE study.
abstract: BACKGROUND
  Infection with human papillomavirus (HPV) is causally linked to the development of anal and cervical cancer. In the United States, the incidence of anal cancer among men who have sex with men (MSM) is higher than the incidence of cervical cancer among women. Anal squamous intraepithelial lesions (ASILs) are anal cancer precursors comprising low-grade squamous intraepithelial lesions (LSILs) and high-grade squamous intraepithelial lesions (HSILs). The prevalence of cervical cancer precursor lesions peaks at around 30 years of age. The age-related prevalence of ASILs in HIV-negative MSM is unknown.
  
  
  METHODS
  We conducted a cross-sectional analysis of the prevalence and determinants of ASILs in 1262 HIV-negative MSM aged 18-89 years recruited from four U.S. cities. Anal cytology and behavioral data were obtained. Anal HPV infection status was assessed by polymerase chain reaction. Independent predictors of ASILs were identified using logistic regression. All statistical tests were two-sided.
  
  
  RESULTS
  The prevalences of LSILs and HSILs were 15% and 5%, respectively, and did not change with age. In a multivariable analysis, the risk of LSILs was associated with having more than five male receptive anal sex partners (P = .03), any use of poppers (alkyl nitrites) in the previous 6 months [odds ratio (OR) = 1.6, 95% confidence interval (CI) = 1.1 to 2.5; P = .03] or use of injection drugs two or more times per month during the previous 6 months [OR = 19, 95% CI = 1.3 to 277; P = .03], older age at first receptive anal intercourse (P = .004), and infection with a greater number of HPV types (P < .001 for linear trend). The risk of HSILs was associated with any anal HPV infection (OR = 3.2, 95% CI = 1.1 to 9.4; P = .039) and infection with an increasing number of HPV types (P < .001 for linear trend).
  
  
  CONCLUSIONS
  Sexually active HIV-negative MSM in all age groups have a high prevalence of ASILs, possibly reflecting their ongoing sexual exposure to HPV.
authors.affiliation: Department of Medicine, University of California-San Francisco, CA 94143-0654, USA. pvch@itsa.ucsf.edu
authors.forename: Peter V
authors.initials: PV
authors.lastname: Chin-Hong
authors.forename: Eric
authors.initials: E
authors.lastname: Vittinghoff
authors.forename: Ross D
authors.initials: RD
authors.lastname: Cranston
authors.forename: Lynette
authors.initials: L
authors.lastname: Browne
authors.forename: Susan
authors.initials: S
authors.lastname: Buchbinder
authors.forename: Grant
authors.initials: G
authors.lastname: Colfax
authors.forename: Maria
authors.initials: M
authors.lastname: Da Costa
authors.forename: Teresa
authors.initials: T
authors.lastname: Darragh
authors.forename: Dana Jones
authors.initials: DJ
authors.lastname: Benet
authors.forename: Franklyn
authors.initials: F
authors.lastname: Judson
authors.forename: Beryl
authors.initials: B
authors.lastname: Koblin
authors.forename: Kenneth H
authors.initials: KH
authors.lastname: Mayer
authors.forename: Joel M
authors.initials: JM
authors.lastname: Palefsky
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging; D001005:Anus Neoplasms / Q000453:epidemiology* / Q000473:pathology / Q000821:virology; D002294:Carcinoma, Squamous Cell / Q000453:epidemiology* / Q000473:pathology / Q000821:virology; D003430:Cross-Sectional Studies; D005260:Female; D018451:Homosexuality, Male; D006801:Humans; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D027383:Papillomaviridae / Q000302:isolation & purification; D030361:Papillomavirus Infections / Q000150:complications / Q000453:epidemiology*; D011230:Precancerous Conditions / Q000453:epidemiology* / Q000473:pathology / Q000821:virology; D015995:Prevalence; D012307:Risk Factors; D012725:Sexual Behavior; D014481:United States / Q000453:epidemiology; D002583:Uterine Cervical Neoplasms / Q000453:epidemiology