Outcomes after (chemo)radiotherapy for anal cancer - A nationwide cohort study.

Introduction: Due to the rarity of anal cancer, real-world data on treatment outcomes are scarce. However, its incidence is increasing in the Netherlands with > 300 new cases and 70 deaths yearly. Standard of care consists of chemoradiotherapy (CRT) or radiotherapy alone (RT). The primary objective of our nationwide study was two-fold; to evaluate real-world outcomes after curatively intended CRT/RT for anal squamous cell carcinoma (ASCC), and to create a large, high-quality dataset as a national benchmark to guide future prospective research. Material and methods: Data were collected retrospectively from 16 Dutch institutions treating ASCC between 2015 and 2018. Primary endpoint was locoregional recurrence free survival (LRFS). Secondary endpoints were overall survival (OS), disease specific survival (DSS), colostomy free survival (CFS), complete response (CR) and toxicity. Results: A total of 462 patients were analysed. Most patients received CRT (85%), with mitomycin-capecitabine as a radiosensitizer in 86% of cases. After median follow-up of 5 years, LRFS for all patients was 80% at 3 years and 78% at 5 years. In total 82% of patients had reached CR, with a median interval to define CR of 3 months. At 3 years, OS, DSS and CFS were 78%, 86% and 88%, respectively. Conclusion: These real-world data demonstrate that curatively intended CRT/RT for ASCC results in LRFS of 80% at 3 years. Organ preservation outcomes were favourable with a CFS of 88% at 3 years. These findings support the current treatment approach as the reference standard for these patients and provide a national benchmark to guide future prospective research.