Defining the actinic keratosis field: a literature review and discussion

Abstract

Despite the chronic and increasingly prevalent nature of actinic keratosis (AK) and existing evidence supporting assessment of the entire cancerization field during clinical management, a standardized definition of the AK field to aid in the understanding and characterization of the disease is lacking. The objective of this review was to present and appraise the available evidence describing the AK cancerization field, with the aim of determining a precise definition of the AK field in terms of its molecular (including genetic and immunological), histological and clinical characteristics. Eight European dermatologists collaborated to conduct a review and expert appraisal of articles detailing the characteristics of the AK field. Articles published in English before August 2016 were identified using PubMed and independently selected for further assessment according to predefined preliminary inclusion and exclusion criteria. In addition, a retrospective audit of patients with AK was performed to define the AK field in clinical terms. A total of 32 review articles and 47 original research articles provided evidence of sun-induced molecular (including genetic and immunological) and histological skin changes in the sun-exposed area affected by AK. However, the available literature was deemed insufficient to inform a clinical definition of the AK field. During the retrospective audit, visible signs of sun damage in 40 patients with AK were assessed. Telangiectasia, atrophy and pigmentation disorders emerged as 'reliable or very reliable' indicators of AK field based on expert opinion, whereas 'sand paper' was deemed a 'moderately reliable' indicator. This literature review has revealed a significant gap of evidence to inform a clinical definition of the AK field. Therefore, the authors instead propose a clinical definition of field cancerization based on the identification of visible signs of sun damage that are reliable indicators of field cancerization based on expert opinion.

Actinic keratosis and surrounding skin exhibit changes in corneocyte surface topography and decreased levels of filaggrin degradation products

“…Existing subclinical changes can explain the local recurrence, eruption of new AKs or development of SCC in the same area. Therefore, recent European consensus recommendations and expert opinions emphasize the need to treat not only the visible AK lesion, but also the subclinical AK . While conventional biopsy and histopathological analysis are still regarded as the gold standard for identifying pathophysiological features of AK, this approach is not feasible for larger skin areas .…”

“…Often on sun‐exposed skin sites, multiple AKs are present, and the recurrence rate and development of new AK is high, which can be explained by existence of a so‐called field of cancerization (FoC), an area around the AK which shows subclinical alterations . Therefore, several guidelines recommend treatment should not only be focused on the visible lesion, but also include an entire sun‐exposed field preventing recurrence and development of new AK lesions. In contrast to “lesion‐directed treatments,” including cryotherapy, laser therapy, curettage and dermabrasion, several therapeutic options are available which are “field‐directed” such as retinoids, imiquimod, 5‐fluorouracil, photodynamic therapy, diclofenac and ingenol mebutate .…”

The more the better? An appraisal of combination therapies for actinic keratosis

“…Visible AK lesions are often surrounded by tissue that harbours significant UV‐induced histologic and genetic alterations but appears clinically unaltered. This so‐called field cancerization is a commonly observed phenomenon in chronically sun‐damaged skin and requires appropriate treatment approaches . Although the risk is presumably low for single lesions, AK can progress to cutaneous squamous cell carcinoma (cSCC) .…”

Cryosurgery combined with topical interventions for actinic keratosis: a systematic review and meta‐analysis

“…Visible AK lesions may be surrounded by tissue that clinically appears unaltered but bears significant ultraviolet‐induced histological and genetic abnormalities. This concept has generally been accepted as field cancerization, although an exact clinical definition has not yet been coined …”