title: Underestimation of relative risks by standardized incidence ratios for AIDS-related cancers.
abstract: OBJECTIVE
  Registry-based studies provide valuable data regarding cancer risk among people with HIV/AIDS (PWHA). Such studies utilize the standardized incidence ratio (SIR) to estimate the relative risk (RR), an etiologically relevant measure. However, SIR may underestimate RR when HIV/AIDS prevalence in the general population or RR is high. We quantified the extent of this underestimation for 3 AIDS-related cancers: Kaposi sarcoma (KS), central nervous system non-Hodgkin lymphoma (CNS NHL) and cervical cancer.
  
  
  METHODS
  We used data on cancer risk among PWHA from the U.S. HIV/AIDS Cancer Match Study. SIRs were compared with RRs estimated using two methods: (1) SIRs calculated using pre-AIDS era (1973-1979) cancer incidence rates (SIRpre-AIDS) and (2) SIRs calculated after subtraction of cancers known to be among PWHA from general population rates (SIRexclusion).
  
  
  RESULTS
  For KS and CNS NHL, SIRs (117.8 and 133.9, respectively) calculated using overall general population rates substantially underestimated both SIRpre-AIDS (19,778 and 3,612, respectively) and SIRexclusion (657.7 and 536.4, respectively). In contrast, the extent of underestimation was negligible for cervical cancer (SIR = 4.9 vs. SIRexclusion = 5.1). For KS and CNS NHL, SIRs were higher in females than in males. However, SIRpre-AIDS and SIRexclusion estimates were more similar, indicating that SIR differences artifactually reflect differences in HIV/AIDS prevalence between males and females. For KS and CNS NHL, trends across calendar time were weaker in SIRs than in SIRpre-AIDS and SIRexclusion.
  
  
  CONCLUSIONS
  For KS and CNS NHL, SIRs substantially underestimate RRs. This underestimation arises from the exceptionally high relative risk of KS and CNS NHL among PWHA. SIRs must be interpreted cautiously when HIV/AIDS prevalence is high or varies across groups of interest.
authors: Viral Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, 6120 Executive Blvd, EPS 7072, Rockville, MD 20852, USA. chaturva@mail.nih.gov <chaturva@mail.nih.gov>
authors: Anil K
authors: AK
authors: Chaturvedi
authors: Sam M
authors: SM
authors: Mbulaiteye
authors: Eric A
authors: EA
authors: Engels
mesh_terms: D016543:Central Nervous System Neoplasms / Q000453:epidemiology*; D005260:Female; D015658:HIV Infections / Q000150:complications*; D006801:Humans; D015994:Incidence; D016483:Lymphoma, AIDS-Related / Q000453:epidemiology*; D008228:Lymphoma, Non-Hodgkin / Q000453:epidemiology*; D008297:Male; D008498:Medical Record Linkage; D016012:Poisson Distribution; D015995:Prevalence; D012042:Registries; D012306:Risk; D012514:Sarcoma, Kaposi / Q000453:epidemiology*; D014481:United States / Q000453:epidemiology; D002583:Uterine Cervical Neoplasms / Q000453:epidemiology*