Survival benefits and predictors of use of chemoradiation compared with radiation alone for early stage (T1-T2N0) anal squamous cell carcinoma

Background: Standard of care treatment for anal squamous cell carcinoma (SCC) is concurrent chemoradiation (CRT). However, the necessity of CRT over radiation alone for T1-2N0 disease is less certain. Methods: The National Cancer Database (NCDB) was queried to identify patients who received CRT, defined as initiation of chemo and RT within 14 days of each other, or RT alone (without any chemo during initial treatment phase) for cT1-2N0M0 SCC of the anus. The cohort was limited to patients less than 70 years old with Charlson-Deyo Comorbidity Index of 0, receiving a radiation dose range of 4,500-5,940 cGy. Univariable and multivariable logistic regression were performed to assess for predictors of CRT usage. Five-year overall survival (OS) was analyzed using the Kaplan-Meier method with the log rank test both for the full cohort and then on the subsets of T1 and T2 patients. Results: We identified 4,564 patients, of whom 4,371 (95.8%) received CRT and 193 (4.2%) received RT alone. Median follow up was 49.8 months. About 33.5% of patients had cT1N0 disease, while 66.5% of patients had cT2N0 disease. On multivariable logistic regression, patients were more likely to receive CRT if they had T2 disease [OR 2.318 (1.732-3.102), P<0.0001]. Five-year OS was 86.6% for CRT and 79.1% for RT (P=0.001). For T1 patients, 5-year OS was 90.3% with CRT and 84.7% with RT (P=0.114). For T2 patients, 5-year OS was 84.7% with CRT and 72.8% with RT (P<0.0001). Multivariable Cox regression analysis confirmed association between OS and CRT use [HR 0.588 (95% CI: 0.430-0.804), P=0.001]. Conclusions: The vast majority of patients under age 70 without significant comorbidities are treated with CRT over radiation alone for early stage anal SCC, with better survival associated with CRT.