There is no consensus on the indication of postoperative radiotherapy for early stages oral and oropharyngeal squamous cell carcinoma with complete pathological resection and no neck node metastasis, but most of the institutions do not give any post-operative treatment. Loco-regional control rates range between 80-85% at five years. Surgical margins molecular analysis for microsatellite instability (MSI) marker could help to select the high-risk patients who should receive postoperative radiotherapy. We expect to include 120 patients in five years and have 60 informative tumors for MSI marker. Patients with positive molecular margins will receive postoperative radiotherapy (50 Gy). Patients with negative molecular margins will not receive radiotherapy.