Definitive Intensity-Modulated Chemoradiation for Anal Squamous Cell Carcinoma: Outcomes and Toxicity of 428 Patients Treated at a Single Institution

Although rare, the incidence of squamous cell carcinoma of the anus continues to rise. This retrospective report describes outcomes and toxicities after intensity-modulated radiation therapy-based chemoradiation for the treatment of squamous cell carcinoma of the anus, evaluates the impact of dose escalation, and compares concurrent fluoropyrimidine in combination with either mitomycin or with cisplatin as chemosensitizers. Background Although intensity-modulated radiation therapy (IMRT) is considered the standard of care for the treatment of squamous cell carcinoma of the anus (SCCA), few large series have reported oncologic outcomes and toxicities. In this retrospective report, we aim to describe outcomes and toxicities after IMRT-based chemoradiation (CRT) for the treatment of SCCA, evaluate the impact of dose escalation (>54 Gy), and compare concurrent fluoropyrimidine in combination with either mitomycin or with cisplatin as chemosensitizers. Methods Patients treated at The University of Texas MD Anderson Cancer Center between January 1, 2003 and December 31, 2018 with IMRT-based CRT were included. Median time to locoregional recurrence, time to colostomy, and overall survival were estimated using the Kaplan-Meier method. Results A total of 428 patients were included; median follow-up was 4.4 years. Three hundred and thirty-four patients (78.0%) were treated with concurrent cisplatin and fluoropyrimidine, and 160 (37.4%) with >54 Gy. Two- and 5-year freedom from locoregional failure, freedom from colostomy failure, and overall survival were 86.5% and 81.2%, respectively, 90.0% and 88.3%, respectively, and 93.6% and 85.8%, respectively. Neither dose escalation nor mitomycin-based concurrent chemotherapy resulted in improved outcomes. Mitomycin-based concurrent chemotherapy was associated with in approximately 2.5 times increased grade 3 or greater acute toxicity. Radiation dose >54 Gy was associated with approximately 2.6 times increased Grade 3 or greater chronic toxicity. Conclusions Our results suggest IMRT-based CRT with concurrent fluoropyrimidine and cisplatin is a safe and feasible option for patient with SCCA and may cause less acute toxicity. The role for radiation dose escalation is unclear and requires further study.