A 55-year-old farmer from rural India presents with a 1.5 cm erythematous, scaly, indurated plaque on the lower lip with a history of chronic sun exposure and tobacco use. Histopathology confirms moderately differentiated squamous cell carcinoma. The lesion is localized without nodal involvement. Surgery is planned, but the patient also wishes adjuvant topical therapy to reduce recurrence risk. What is the drug of choice for adjuvant topical application?