Abstract / Summary
Multimodal imaging with pelvic MRI and FDG PET/CT is currently recommended for staging anal squamous cell carcinoma (ASCC). However, accumulating data suggest that PET/CT frequently alters staging and radiotherapy planning, raising questions about whether routine MRI is necessary for all patients. To evaluate whether a PET/CT-first staging strategy provides sufficient diagnostic information for most patients with ASCC, with MRI reserved for cases where detailed local anatomy may affect radiotherapy planning, multidisciplinary decision-making, or serve as a baseline for potential subsequent surgical planning. Narrative review and synthesis of current guideline recommendations and published studies on the added diagnostic and management benefits of PET/CT compared to MRI in initial ASCC staging. Across multiple studies, PET/CT changed TNM staging in about 20–40% of patients and influenced management in up to 20–30%, mainly through nodal upstaging and adjusting radiotherapy fields. Conversely, MRI’s additional impact on initial treatment intent may be more limited, as most stage I–III patients proceed to definitive chemoradiotherapy regardless of detailed T-stage refinement. PET/CT also allows for whole-body assessment, detecting occult distant metastatic disease and guiding radiotherapy dose and target volume planning. While MRI retains clear value for evaluating invasion of adjacent organs, fistulising disease, and as a pre-treatment baseline for potential salvage surgery, its routine application to all patients warrants reconsideration. A PET/CT-first staging pathway with selective use of MRI represents a testable hypothesis that warrants prospective evaluation. Prospective studies assessing oncologic, workflow, and health-economic outcomes are needed to determine its value. Question Does routine pelvic MRI add sufficient management value to justify its universal use alongside FDG PET/CT in the staging of ASCC? Findings PET/CT altered TNM staging in ~22% and management in ~20% of anal cancer patients following MRI, predominantly through nodal upstaging and radiotherapy modification . Relevance statement A PET/CT-first staging strategy with selective MRI use is proposed for prospective evaluation, potentially improving efficiency and equity of staging in ASCC.