A 52-year-old man presents with a 2.5 cm pigmented lesion on his back with irregular borders and mixed colors. Biopsy confirms cutaneous melanoma with a Breslow thickness of 3.2 mm and no ulceration. He is found to be BRAF V600E mutation-positive on molecular testing. After complete staging shows no distant metastases (Stage IIIB), he undergoes wide local excision and sentinel lymph node biopsy. What is the drug of choice for adjuvant therapy in this patient?