A 60-year-old man with actinic keratoses on sun-exposed skin develops a firm, indurated nodule on the lower lip that ulcerates. Biopsy shows nests of squamous epithelium with central keratin pearls and individual cell dyskeratosis invading into the dermis. The most important distinguishing feature from actinic keratosis is:
- A Presence of nuclear atypia in basal keratinocytes
- B Dermal invasion breaching the basement membrane ✓
- C Full-thickness epidermal dysplasia
- D Solar elastosis in underlying dermis
Correct answer: B. Dermal invasion breaching the basement membrane
Explanation
Squamous cell carcinoma (SCC) of skin is distinguished from its precursor actinic keratosis by invasion through the basement membrane into the dermis. Actinic keratosis shows atypical keratinocytes confined to the epidermis (in situ), while SCC shows dermal invasion with desmoplastic stromal reaction. Keratin pearls (squamous eddies) and individual cell dyskeratosis confirm squamous differentiation. SCC of the lip and ear carries higher metastatic risk than SCC at other cutaneous sites.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.