Long-term follow-up experience in anal canal cancer treated with Intensity-Modulated Radiation Therapy: Clinical outcomes, patterns of relapse and predictors of failure

•IMRT for anal cancer is efficient in the long-term with manageable toxicity.•Advanced T-stage remains the main prognostic factor for survival.•Planned gaps and prolonged treatment breaks should be avoided.•Locoregional failures mostly occur in-field suggesting radioresistance.•Novel systemic strategies are needed to improve distant control.