The patient likely has a squamous cell carcinoma (SCC), which is the second most common type of skin cancer, and skin biopsy is the appropriate next step in management. Risk factors for SCC are smoking and sun exposure, as in this patient; other risk factors include human papillomavirus infection, immunosuppression, and arsenic exposure. Prompt recognition of SCCs is crucial for optimizing patient outcomes since these lesions can grow rapidly and occasionally metastasize. Lesions on the lip are particularly aggressive and are associated with worse outcomes. The relatively large size of this patient's lesion and tenderness both suggest a malignancy rather than a precancerous lesion. SCCs can sometimes resemble infectious processes such as furuncles, mycobacterial infections, or fungal infections; however, the patient's clinical presentation is most consistent with an SCC, and thus a skin biopsy would be crucial for diagnosis.

Tissue culture for bacteria would not yield useful diagnostic information and may confuse the diagnosis since SCCs are often colonized by bacteria.

Cryotherapy and topical 5-fluorouracil are used for the treatment of precancerous lesions (actinic keratoses) and occasionally SCC in situ, but would not be an appropriate choice for this patient since the lesion appears to be an invasive SCC in a high-risk site.

Similarly, electrodesiccation and curettage may be used for SCC in situ and in certain settings for low-risk well-differentiated SCCs, but would not be an appropriate choice for this location, particularly prior to obtaining a tissue diagnosis.