Intensity Modulated Radiotherapy for Anal Canal Squamous Cell Carcinoma: A 16-year Single Institution Experience

Introduction: To report long-term efficacy and adverse events (AEs) associated with intensity modulated radiotherapy (IMRT) for patients with anal canal squamous cell carcinoma (ASCC).

Materials And Methods: This was a retrospective review of patients with ASCC who received curative-intent IMRT and concurrent chemotherapy (98%) between 2003 and 2019. Overall survival (OS), colostomy-free survival (CFS), and progression-free survival (PFS) were estimated using the Kaplan-Meier method. The cumulative incidence of local recurrence (LR), locoregional recurrence (LRR), and distant metastasis (DM) were reported. Acute and late AEs were recorded per National Cancer Institute Common Terminology Criteria for AEs.

Results: 127 patients were included. The median patient age was 63 years (interquartile range [IQR] 55-69) and 79% of patients were female. 33% of patients had T3-4 disease and 68% had clinically involved pelvic or inguinal lymph nodes (LNs).The median patient follow-up was 47 months (IQR: 28-89 months). The estimated 4-year OS, CFS, and PFS were 81% (95% confidence interval [CI]: 73%-89%), 77% (95% CI: 68%-86%), and 78% (95% CI: 70%-86%), respectively. The 4-year cumulative incidences of LR, LRR, and DM were 3% (95% CI: 1%-9%), 9% (95% CI: 5%-17%), and 10% (95% CI: 6%-18%), respectively. Overall treatment duration greater than 39 days was associated with an increased risk of LRR (Hazard Ratio [HR]: 5.2, 95% CI: 1.4-19.5, p = 0.015). The most common grade 3+ acute AEs included hematologic (31%), gastrointestinal (GI) (17%), dermatologic (16%), and pain (15%). Grade 3+ late AEs included: GI (3%), genitourinary (GU) (2%), and pain (1%). Current smokers were more likely to experience grade 3+ acute dermatologic toxicity compared to former or never smokers (34% vs. 7%, p < 0.001).

Conclusions: IMRT was associated with favorable toxicity rates and long-term efficacy. These data support the continued utilization of IMRT as the preferred treatment technique for patients with ASCC.