Pharmacokinetics of LEO 43204 Gel in Actinic Keratosis Administered Under Maximal Use Conditions

Inclusion Criteria: 1. Subjects with 15 or more clinically typical, visible and discrete AKs on either: * Full face (corresponding to a treatment area of at least 250 cm2). If subjects have a beard they must shave no later than the day before the first drug application. * A contiguous area of approximately 250 cm2 on the arm between wrist and shoulder. * Balding scalp (corresponding to a treatment area of approximately 250 cm2). Subjects with sparse hair on the scalp can be enrolled as long as LSR and AK assessments are not compromised. 2. Subject at least 18 years of age. 3. Female subjects of childbearing potential\* must be confirmed not pregnant by a negative urine pregnancy test prior to trial treatment. 4. Female subjects of childbearing potential must be willing to use effective contraception at trial entry and until completion. Exclusion Criteria: 1. Location of the treatment area (full face, full balding scalp, chest, trunk or extremities) * within 5 cm of an incompletely healed wound. * within 5 cm of a suspected basal cell carcinoma (BCC) or SCC. 2. Previously assigned treatment in this clinical trial or previously participated in a clinical trial in the LEO 43204 programme. 3. Lesions in the treatment area that have: atypical clinical appearance (e.g. cutaneous horns)and/or, recalcitrant disease (e.g., did not respond to cryotherapy on two previous occasions).