Background: Actinic keratoses (AKs) are considered to be a 'field of cancerization' consisting of a histologicallyabnormal epithelium adjacent to tumour tissue. Treatment of the 'field of canceri-zation' is important for the prevention ofneoplasm progression. UV radiation, especially UVB, produce genotoxic photoproducts such as cyclobutane pyrimidinedimers (CPDs) and 6-4 photo-products (6-4PPs) in DNA, being major players in skin cancerization. The potential useof DNA photolyases in skin cancer prevention is increasingly being demonstrated. Topical application of a liposomeformulation containing CPD photolyase onto human skin provides protection against UV-B-induced damages.

Objectives: To assess the effects of topical application of a medical device (Eryf-AK) containing a DNA-repairenzyme, photolyase, encapsulated in liposomes and UV filters, on cancerization field in actinic keratosis (AK).

Methods: 13 AK patients were included. Clinical, dermoscopic, and reflectance confocal microscopy (RCM)assessments, as well as skin biopsies, before and after a 4-week treatment were performed. Patients used Eryf-AKtwice daily or only a sunscreen (3:1) with a similar sun protection factor (SPF) for one month.

Results: Erythema and scaling improved with Eryf-AK. RCM showed a reduction in scaling, detached corneocytesand polygonal nucleated cells in the stratum corneum (p=0.004, p=0.018, and p=0.021), an improvement of the atypicalhoneycomb pattern, and a decreased number of round nucleated cells at the spinous granulous layer (p<0.0005and p=0.019) with Eryf-AK while no improvement was noted with the sunscreen product. The mean RCM score forAK significantly improved from 0.78 to 0.27 (p=0.002) with Eryf-AK. Histological clearance of AK in 4 cases and animprovement with a focal AK associated with inflammation in 3 additional patients were also observed with Eryf-AK. Adecrease in p21 expression (p=0.042) and a tendency to decrease PCNA expression was also observed with Eryf-AK(p=0.076).

Conclusion: Our results show a benefit from Eryf-AK in the treatment of AK cancerisation field. The improvementwas demonstrated clinically, by RCM, histologically and by immunohistochemistry. An improvement was also observedin the two patients with xeroderma pigmentosum, suggesting a benefit from this topical treatment in patients with thisrare genetic disorder.