A patient who consumes alcohol daily has a lip lesion with the clinical features of squamous cell carcinoma. From which epithelial layer does this malignancy arise?

Correct answer: A. Stratum spinosum

• A. CORRECT. SQUAMOUS cell carcinoma arises from the SQUAMOUS (prickle) cells of the STRATUM SPINOSUM — the layer that gives the tumour its name and its characteristic differentiated features on histology: intercellular bridges, individual cell keratinisation, and keratin pearls. Dysplasia begins in the basal region and progresses upward, but the malignant cells that define SCC are of spinous-layer type.
• B. The stratum corneum is the anucleate keratinised surface layer. It is a product of differentiation, not a proliferative compartment from which tumours arise.
• C. The stratum basale is where BASAL CELL CARCINOMA arises — a tumour of the skin that essentially never occurs on the oral mucosa. This is the classic distractor.
• D. The stratum granulosum contains keratohyalin granules and is a transitional differentiating layer, not the origin of SCC.

Note: Lip SCC has a strong association with actinic damage (lower lip vermilion), tobacco and alcohol. Alcohol and tobacco together are synergistic, not merely additive.