Patients with T1-2 N0 anal squamous cell carcinoma benefit significantly from adjuvant radiation therapy after local excision.

• Five-year overall survival rates were 82.8% with radiation versus 74.9% without (p < .001).
• The benefit was especially marked in those with positive surgical margins (79.9% vs 67.2%; p = .003) and in women ≥65 years (85.8% vs 72.2%; p < .001).

Incorporating adjuvant radiation could be critical for improving outcomes in high-risk subgroups of these patients.

• Omitting treatment increased overall mortality by 40% (HR 1.4; p < .001).