Field cancerisation
Field change; field effect; sun-damaged field; cancerisation field
Field cancerisation describes the multifocal, clonally diverse preneoplastic change that develops across chronically UV-damaged skin — typically the scalp, forehead, dorsal hands and forearms of older adults and OTRs. Multiple actinic keratoses arise from the same field of genetically altered keratinocytes; even cleanly excised cSCCs leave a residual field at risk of further tumour development. Field-directed therapy (topical 5-fluorouracil, imiquimod, tirbanibulin, MAL-PDT, daylight PDT) treats clinical and subclinical AKs in one area and reduces subsequent cSCC incidence in randomised trials. Field management is the practical strategy for older or immunosuppressed patients with multiple, recurrent or progressing AKs.
The concept
- Chronic UV exposure produces clonal expansion of p53-mutant keratinocytes across a contiguous field of skin, with multiple foci of dysplasia and clinical AKs visible alongside subclinical disease.
- Individual AKs may regress, persist or progress to cSCC; the field itself is the substrate for new tumour formation.
- 5-year cSCC risk on a field with ≥ 5 AKs is approximately 10% (much higher in OTRs).
- Concept informs clinical practice — treat the field, not just individual lesions.
Clinical recognition
- Confluent erythema, scale, telangiectasia and roughness across sun-exposed sites — scalp (especially balding), forehead, temples, ears, cheek, dorsal forearms and hands.
- Multiple AKs of varying thickness within the field.
- Background dermatoheliosis — solar elastosis, solar lentigines, sebaceous hyperplasia.
- Dermoscopy of AK in the field — strawberry pattern, scale, dotted vessels.
Field-directed topical therapy
- Topical 5-fluorouracil 5% (Efudix) — twice daily for 3–4 weeks; brisk inflammatory reaction. See topical 5-FU.
- Topical imiquimod 5% (Aldara) or 3.75% — TLR-7 agonist; 3 times weekly for 4 weeks (5%) or daily for 2 + 2 weeks (3.75%). See topical imiquimod.
- Tirbanibulin 1% (Klisyri) — once daily for 5 days; less inflammatory, better cosmetic tolerability. See tirbanibulin.
- Diclofenac 3% (Solaraze) — gentler but less efficacious; twice daily for 60–90 days.
Photodynamic therapy
- Methyl-aminolaevulinate (MAL)-PDT — porphyrin photosensitiser applied to the field, activated by red light. Highly effective; significant pain during illumination.
- Daylight PDT — sunscreen + MAL applied; patient sits outdoors in daylight for 2 hours. Comparable efficacy to conventional PDT with markedly less pain. UK summer / spring conditions adequate.
- See photodynamic therapy.
Evidence and cSCC reduction
- VA Topical Tretinoin Chemoprevention Trial (Weinstock 2009) — modest cSCC reduction; high adverse effects.
- Jansen et al. (NEJM 2019) — head-to-head trial of 4 field therapies; 5-FU most effective at 12 months.
- Multiple field-treatment cycles often required — most patients return for repeat treatment every 1–2 years.
- OTR-specific evidence — field therapy combined with reduction of immunosuppression where possible; acitretin chemoprophylaxis for high-burden OTR.
References
- Slaughter DP, Southwick HW, Smejkal W. "Field cancerization" in oral stratified squamous epithelium. Cancer; 1953 (original).
- Jansen MHE et al. Randomized trial of four treatment approaches for actinic keratosis. N Engl J Med; 2019;380:935–46.
- de Berker D, McGregor JM, Hughes BR. British Association of Dermatologists' guidelines for the care of patients with actinic keratosis 2017. Br J Dermatol. 2017;176(1):20-43.
- Keohane SG et al. British Association of Dermatologists guidelines for the management of people with cutaneous squamous cell carcinoma 2020. Br J Dermatol. 2021;184(3):401-414.
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