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Actinic keratosis and cutaneous squamous cell carcinoma (SCC)
Actinic keratosis (AK) is a premalignant lesion of sun-damaged keratinocytes and cutaneous SCC is its invasive continuation; any skin with cumulative sun damage is a "field" that needs whole-field treatment and follow-up.
Why it matters in the exam
Exam stems show an older patient with rough "sandpaper" lesions on a bald scalp or the backs of the hands, or a kidney transplant recipient with many fast-growing scaly lesions. The question turns on when to biopsy, which field treatment to choose, who is high risk (immunosuppression, lip, ear, chronic scar) and how keratoacanthoma relates to SCC. Risk factors include cumulative sun exposure, fair skin, older age, HPV in some cases, radiation and drugs such as voriconazole. These patients need daily sun protection, periodic skin checks and teaching to recognise a lesion that grows, hurts or bleeds. Oral nicotinamide modestly reduces new lesions in high-risk patients, and daily sunscreen reduces new AKs.
Key points
- AKs are rough lesions on sun-exposed skin and mark a field of sun damage with a risk of SCC.
- Single lesions are treated with cryotherapy, and a wide field with 5-FU, imiquimod or PDT.
- Invasive SCC is a growing, tender keratotic nodule; keratoacanthoma is managed the same way.
- High risk includes lip, ear, chronic scar, immunosuppression, large size, deep invasion and perineural invasion.
- Low-risk SCC is excised with 4–6 mm margins; high-risk SCC needs Mohs, nodal assessment and radiotherapy, and advanced disease cemiplimab.
Summary table
| Lesion | Clinical feature | Significance | Treatment |
|---|---|---|---|
| Actinic keratosis (AK) | Rough, scaly, reddish papule on sun-exposed skin; felt more than seen | Premalignant; small annual transformation risk per lesion | Cryotherapy for a single lesion; 5-FU, imiquimod or PDT for the field |
| SCC in situ (Bowen disease) | Well-demarcated red scaly plaque, often on the legs or trunk | Intra-epidermal, no invasion | 5-FU, PDT, curettage or excision |
| Invasive SCC | Keratotic, tender, rapidly growing papule or nodule, sometimes ulcerated | Risk of lymph-node metastasis, mainly in high-risk lesions | Excision with 4–6 mm margins; Mohs when high risk |
| Keratoacanthoma | Dome-shaped nodule with a central keratin plug, grows over weeks | Regarded as an SCC variant; cannot be reliably distinguished | Excise like SCC |
| High-risk SCC | Lip, ear, scar or chronic ulcer (Marjolin ulcer), immunosuppression, perineural invasion | Higher metastasis and mortality | Mohs, nodal assessment, adjuvant radiotherapy; cemiplimab in advanced disease |
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Sources
- NCCN Guidelines Squamous Cell Skin Cancer, 2025 — Risk stratification and treatment
- British Association of Dermatologists guideline for actinic keratosis, 2017 — Field treatment
- EADV/EDF/EORTC European consensus on cutaneous squamous cell carcinoma, 2023 — Diagnosis and treatment
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.