A 68-year-old farmer from rural Maharashtra presents with a non-healing ulcer on the dorsum of his left hand for 8 months. He reports the lesion began as a small nodule that gradually enlarged and ulcerated. On examination, there is a 2.5 cm × 2 cm indurated ulcer with raised, everted edges and a granulating base. The surrounding skin shows multiple actinic keratoses. Histopathology reveals nests of atypical squamous cells infiltrating the dermis with keratinization. Regional lymph nodes are not palpable. What is the most appropriate next step in management?