A 55-year-old immunocompromised patient (CD4 count 180 cells/μL, on antiretroviral therapy) presents with a 1.5 cm indurated, hyperkeratotic nodule on the lower lip with a history of rapid growth over 3 weeks. Incisional biopsy shows poorly differentiated squamous cell carcinoma with evidence of lymphovascular invasion and perineural invasion. Clinical examination reveals no palpable cervical lymph nodes. What is the most appropriate next step in management?