Oral squamous cell carcinoma arises from which layer of the epithelium?

Correct answer: A. The stratum spinosum

• A. CORRECT. Squamous cell carcinoma arises from the SPINOUS (prickle) CELL LAYER — the stratum spinosum — which is the layer whose cells the tumour recapitulates, showing intercellular bridges and keratin pearl formation. The name itself derives from this: 'squamous' cells with desmosomal 'prickles'.
• B. The stratum granulosum is a thin transitional layer containing keratohyalin granules and is not the origin of squamous cell carcinoma.
• C. The stratum corneum is the superficial layer of dead, anucleate keratinised cells. It is a terminal product, not a proliferative compartment, and no malignancy arises from it.
• D. The lamina propria is CONNECTIVE tissue beneath the epithelium. Malignancies arising there are mesenchymal — fibrosarcoma, Kaposi sarcoma — not carcinomas.

Note: Note the contrast with BASAL CELL CARCINOMA, which arises from the stratum BASALE and occurs on sun-exposed skin, essentially never on oral mucosa. Dysplasia is graded by how far up from the basal layer the atypia extends: lower third = mild, lower two-thirds = moderate, full thickness = severe/carcinoma in situ.