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Medical AI Inquiry: You was designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.  Labels: OBJECTIVE, DESIGN, METHODS, RESULTS. Meshes: Adult, Aged, Aged, 80 and over, Anus Neoplasms, Carcinoma, Squamous Cell, Female, HIV Infections, Humans, Immunocompromised Host, Incidence, Male, Middle Aged, Rectal Neoplasms, Risk Factors.
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Rectal squamous cell carcinoma in immunosuppressed populations: is this a distinct entity from anal cancer? Context: 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 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. 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.
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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.