A 67-year-old man undergoes a colonoscopy for investigation of iron deficiency anaemia. A large, ulcerated polypoid lesion is found in the sigmoid colon, and biopsies confirm adenocarcinoma. Staging CT scan shows no evidence of distant metastases, but reveals enlarged pericolic lymph nodes. According to the principles of cancer management, what is the most likely primary curative treatment modality for this patient?