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Rectal squamous cell carcinoma in immunosuppressed populations: is this a distinct entity from anal cancer?
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    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.


    Population-based registry


    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 to 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.


    HIV-infected persons had an excess risk of rectal SCC compared to 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 men who have sex with men (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=1.86; 95%CI 1.04–3.31). Based on available information, one-third of rectal SCCs were determined to be misclassified anal cancer.


    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 tumor location is needed to prove that rectal SCC is a distinct entity.

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  • Funding:
    261201000024C/PHS HHS/United States
    261201300021I/PHS HHS/United States
    5U58/DP003931-02/DP/NCCDPHP CDC HHS/United States
    5U58DP000824-04/DP/NCCDPHP CDC HHS/United States
    5U58DP003875-01/DP/NCCDPHP CDC HHS/United States
    5U58DP003921-03/DP/NCCDPHP CDC HHS/United States
    5U62PS001005-05/PS/NCHHSTP CDC HHS/United States
    N01-PC-2013-00021/PC/NCI NIH HHS/United States
    U58DP000848-04/DP/NCCDPHP CDC HHS/United States
    U62PS004001-2/PS/NCHHSTP CDC HHS/United States
    U62PS004011-02/PS/NCHHSTP CDC HHS/United States
    Z99 CA999999/Intramural NIH HHS/United States
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