A lip lesion that has been growing for six months in a heavy smoker most likely originates from which tissue layer?

A growing lesion on the lip of a heavy smoker, especially one persisting for more than 2-4 weeks, is suspicious for malignant transformation - most likely squamous cell carcinoma (SCC) or actinic keratosis. The lip epithelium (stratified squamous epithelium) is the tissue of origin for these lesions, as SCC arises from keratinocytes in the spinous (squamous) cell layer. The lower lip is particularly susceptible due to sun exposure and tobacco use. Any such lesion warrants biopsy. Actinic cheilitis (precancerous) and SCC of the lip are both epithelium-derived.