The importance of treating the field in actinic keratosis.

Actinic keratoses (AKs) are intraepithelial atypical proliferations of keratinocytes that develop in skin that has undergone long-term exposure to ultraviolet radiation. Given the ageing population and an increasing prevalence of AK, the socio-economic burden of AK is likely to rise over the coming years. Areas of subclinical (non-visible) sun damage in the periphery of visible AK lesions contain the same genetic changes as those found in the lesions themselves, and are known as areas of field cancerization. AK lesions and the field are associated with an increased risk of skin cancer, including invasive squamous cell carcinoma. Although effective in clearing visible AK, lesion-directed therapies do not address field cancerization and can lead to high recurrence rates. In contrast, field-directed therapies, such as ingenol mebutate, imiquimod and diclofenac, can clear both visible and subclinical AK lesions and reduce the development of new lesions in the treated field. Additionally, preclinical studies suggest that field therapy may prevent or delay the recurrence of non-melanoma skin cancer. AK treatment guidelines now recognize the importance of treating the field in patients with AK, and adaptation of treatment guidelines into clinical practice is warranted. Physician and patient education around the consequences of leaving the field of cancerization untreated is necessary in order to reduce the increasing burden associated with AK.