A 48-year-old woman with a history of cutaneous melanoma (Breslow thickness 1.8 mm, Clark level IV, no ulceration) underwent wide local excision 3 years ago. She now presents with a 2 cm firm nodule in the left axilla. Fine-needle aspiration cytology and imaging confirm metastatic melanoma (Stage IIIC). She is BRAF V600E mutation-positive. After lymphadenectomy, what is the drug of choice for adjuvant therapy to reduce the risk of distant recurrence?