Thirty-Two Years of Radiotherapy for T1 Anal Cancer: Patterns, Outcomes, and Side-effects at a Single Institution

Abstract Purpose Definitive chemoradiotherapy is the standard treatment for anal cancer, but the optimal management of small (T1) tumours remains unclear, as these tumours are underrepresented in prospective trials. Methods We retrospectively analysed all patients with T1 anal carcinoma treated with curative intent at the Medical University of Vienna between 1990 and 2022. Patient, tumour, and treatment characteristics were extracted. Outcomes included overall survival (OS), disease-free survival (DFS), colostomy-free survival (CFS), and acute and late toxicity. Kaplan–Meier estimates, log-rank tests, and univariable Cox regression were used for exploratory time-to-event analyses. Results Fifty-five patients (median age 67 years, range 31–86; female/male ratio 2.4:1) were included. The median prescribed dose was 58 Gy; 45% received concurrent chemotherapy and 35% a brachytherapy boost. Five-year OS, DFS, and CFS were 84.7%, 80.1%, and 85.3%, respectively. Late grade 3 toxicity occurred in six patients (11%), exclusively after 2D/3D radiotherapy. No statistically significant OS or DFS differences were demonstrated for brachytherapy, chemotherapy, nodal involvement, or IMRT/VMAT in exploratory univariable analyses. Conclusions Patients with T1 anal carcinoma achieved favourable long-term tumour control and organ preservation after definitive radiotherapy or chemoradiotherapy. Severe late toxicity was observed only after 2D/3D radiotherapy; however, concurrent changes in treatment technique, dose, target volumes, and treatment era preclude attribution of this observation to any single treatment component. Numerically favourable outcomes with brachytherapy and concurrent chemotherapy were observed, but these findings remain hypothesis-generating and require validation in prospective studies.