A collaboration of multidisciplinary experts from the European Association of Dermato-Oncology, the European Dermatology Forum, the European Academy of Dermatology and Venereology, and the European Union of Medical Specialists was formed to develop European recommendations on AK diagnosis and treatment, based on current literature and expert consensus. This guideline addresses the epidemiology, diagnostics, risk stratification and treatments in immunocompetent as well as immunosuppressed patients. Actinic keratoses (AK) are potential precursors of cutaneous squamous cell carcinoma (cSCC) and display typical histopathologic and immunohistochemical features of this malignancy in an early stage. They can develop into cSSC in situ and become invasive in a low percentage of cases. AK is the most frequent neoplasia in white populations, frequently occurring within a cancerous field induced by ultraviolet radiation. Since it cannot be predicted, which lesion will progress to cSCC and when treatment is usually recommended. The diagnosis of AK and field cancerization is made by clinical examination. Dermatoscopy, confocal microscopy, optical coherence tomography or line-field confocal-OCT can help in the differential diagnosis of AK and other skin neoplasms. A biopsy is indicated in clinically and/or dermatoscopically suspicious and/or treatment-refractory lesions. The choice of treatment depends on patients' and lesion characteristics. For single non-hyperkeratotic lesions, the treatment can be started upon patient's request with destructive treatments or topical treatments. For multiple lesions, field cancerization treatment is advised with topical treatments and photodynamic therapy. Preventive measures such as sun protection, self-examination and repeated field cancerization treatments of previously affected skin areas in high-risk patients are advised.

1st Department of Dermatology Aristotle University Thessaloniki Greece

1st Department of Dermatology Venereology National and Kapodistrian University of Athens Andreas Sygros Hospital Athens Greece

Centre for Cell Biology and Cutaneous Research Blizard Institute Barts and The London School of Medicine and Dentistry Queen Mary University of London London UK

Centre for Dermatooncology Department of Dermatology Eberhard Karls University Tuebingen Germany

CentroDerm Clinic Wuppertal Germany

Clinic of Infectious Diseases and Dermatovenereology Centre of Dermatovenereology Vilnius University Vilnius Lithuania

Comprehensive Cancer Center Erlangen European Metropolitan Area of Nuremberg Erlangen Germany

Department of Dermatology and Venereology Sestre Milosrdnice University Hospital Center Zagreb Croatia

Department of Dermatology Copenhagen University Hospital Bispebjerg and Frederiksberg Copenhagen Denmark

Department of Dermatology Faculty of Medicine University of Defence Military Medical Academy Belgrade Serbia

Department of Dermatology Maastricht University Medical Centre Comprehensive Cancer Centre Maastricht The Netherlands

Department of Dermatology Uniklinikum Erlangen Friedrich Alexander University Erlangen Nürnberg Erlangen Germany

Department of Dermatology University Hospital Erasme Université Libre de Bruxelles Brussels Belgium

Department of Dermatology University Hospital Kiel Germany

Department of Dermatology University of Modena and Reggio Emilia Modena Italy

Department of Dermatology Venereology and Allergology Frankfurt University Hospital Frankfurt Germany

Department of Dermatovenereology 3rd Faculty of Medicine Charles University and University Hospital of Kralovske Vinohrady Prague Czech Republic

Department of General and Oncologic Dermatology Ambroise Paré Hospital APHP and EA 4340 Biomarkers in Cancerology and Hemato Oncology UVSQ Université Paris Saclay Boulogne Billancourt France

Department of Oncologic Dermatology Elias University Hospital Bucharest Carol Davila University of Medicine and Pharmacy Bucharest Romania

Department of Pediatric Dermatology Colentina Clinical Hospital Carol Davila University of Medicine and Pharmacy Bucharest Romania

Dermatologia Università Cattolica del Sacro Cuore Rome Italy

Dermatology Clinic Maggiore Hospital Department of Medical Sciences University of Trieste Trieste Italy

Dermatology Department of Biotechnological and Applied Clinical Sciences University of L'Aquila L'Aquila Italy

Dermatology Department of Hospital Clinic of Barcelona IDIBAPS CIBER de Enfermedades Raras Instituto Carlos 3 University of Barcelona Barcelona Spain

Faculty of Health University Witten Herdecke Witten Germany

GROW School for Oncology and Reproduction Maastricht University Maastricht The Netherlands

Nantes Université INSERM CNRS Immunology and New Concepts in ImmunoTherapy INCIT UMR 1302 EMR6001 Nantes France

Skin Cancer Center Azienda Unità Sanitaria Locale IRCCS di Reggio Emilia Reggio Emilia Italy

Skin Cancer Center Department of Dermatology Ruhr University Bochum Bochum Germany

Université Paris Cite AP HP Dermato oncology Cancer institute APHP Nord Paris cité INSERM U976 Saint Louis Hospital Paris France

UOC di Dermatologia Dipartimento di Scienze Mediche e Chirurgiche Addominali ed Endrocrino Metaboliche Fondazione Policlinico Universitario A Gemelli IRCCS Rome Italy

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