title: Rectal squamous cell carcinoma in immunosuppressed populations: is this a distinct entity from anal cancer?
abstract: OBJECTIVE
  Squamous cell carcinoma (SCC) of the rectum is rare, but as with anal cancer, risk may be increased among immunosuppressed individuals. We assessed risk of rectal SCC in HIV-infected people.
  
  
  METHODS
  Population-based registry.
  
  
  METHODS
  We utilized the HIV/AIDS Cancer Match, a linkage of US HIV and cancer registries (1991-2010), to ascertain cases of anal SCC, rectal SCC, rectal non-SCC, and colon non-SCC. We compared risk in HIV-infected persons with the general population using standardized incidence ratios (SIRs) and evaluated risk factors using Poisson regression. We reviewed cancer registry case notes to confirm site and histology for a subset of cases.
  
  
  RESULTS
  HIV-infected persons had an excess risk of rectal SCC compared with the general population (SIR = 28.9; 95% CI 23.2-35.6), similar to the increase for anal SCC (SIR = 37.3). Excess rectal SCC risk was most pronounced among HIV-infected MSM (SIR = 61.2). Risk was not elevated for rectal non-SCC (SIR = 0.88) or colon non-SCC (SIR = 0.63). Individuals diagnosed with AIDS had higher rectal SCC rates than those with HIV-only (incidence rate ratio = 1.92; 95% CI 1.08-3.42). Based on available information, one-third of rectal SCCs were determined to be misclassified anal cancer.
  
  
  CONCLUSIONS
  HIV-infected individuals, especially with advanced immunosuppression, appear to have substantially elevated risk for rectal SCC. As for anal SCC, rectal SCC risk was highest in MSM, pointing to involvement of a sexually transmitted infection such as human papillomavirus. Site misclassification was present, and detailed information on tumour location is needed to prove that rectal SCC is a distinct entity.
authors.affiliation: aDivision of Cancer Epidemiology and Genetics, National Cancer InstitutebColorado Central Cancer Registry, Colorado Department of Public Health and Environment, Denver, ColoradocMichigan Cancer Surveillance Program, Michigan Stage Cancer RegistrydCommunicable Disease Branch, North Carolina Division of Public HealtheNew Jersey State Cancer Registry, New Jersey Department of Health, Trenton, New Jersey, USA.
authors.forename: Anna E
authors.initials: AE
authors.lastname: Coghill
authors.forename: Meredith S
authors.initials: MS
authors.lastname: Shiels
authors.forename: Randi K
authors.initials: RK
authors.lastname: Rycroft
authors.forename: Glenn
authors.initials: G
authors.lastname: Copeland
authors.forename: Jack L
authors.initials: JL
authors.lastname: Finch
authors.forename: Anne M
authors.initials: AM
authors.lastname: Hakenewerth
authors.forename: Karen S
authors.initials: KS
authors.lastname: Pawlish
authors.forename: Eric A
authors.initials: EA
authors.lastname: Engels
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001005:Anus Neoplasms / Q000453:epidemiology*; D002294:Carcinoma, Squamous Cell / Q000453:epidemiology*; D005260:Female; D015658:HIV Infections / Q000150:complications*; D006801:Humans; D016867:Immunocompromised Host; D015994:Incidence; D008297:Male; D008875:Middle Aged; D012004:Rectal Neoplasms / Q000453:epidemiology*; D012307:Risk Factors