Actinic keratosis (AK) is a very common chronic skin disease in which clinical and subclinical skin lesions coexist on sun-exposed areas such as the face, ears, scalp, neck, back of the hands and forearms, and lips.
Although AK is not life-threatening, it is highly prevalent. The American Academy of Dermatology (AAD) diagnoses at least one lesion in 60% of predisposed people over the age of 40. In Europe, prevalence rates vary from 4.7% (in a French cross-sectional study) to 31% (in Austrian individuals aged = 30 years) and up to 37% in the most recent Rotterdam Study, which included a population-based cohort of 2061 elderly individuals.
The main risk factors for AK include chronic exposure to ultraviolet (UV) radiation, use of sunbeds, older age (up to 80% of adults over 60 are affected), male gender, fair skin (Fitzpatrick skin type I-II), prolonged immunosuppression, genetic diseases, and a history of AK lesions or non-melanoma skin cancer.
AK lesions are usually asymptomatic, but can sometimes be associated with symptoms such as itching, burning, bleeding or stinging, which has an impact on the quality of life of those affected.
Typical AK presents clinically as a rough, ill-defined, scaly papule or patch, usually < 1 mm in height or with a cutaneous horn without induration at the base. In contrast, hyperkeratotic AK presents as a rough, ill-defined, spiny papule more than 1 mm in height. Histologically, both AK and hyperkeratotic AK may show atypia of the keratinocytes without extensive atypia of the full thickness of the epidermis and follicles. However, the full-thickness epidermal involvement raises fears of the development of skin cancer. For this reason, treatment is necessary not only to clinically eradicate overt and subclinical lesions, but also to prevent progression to cutaneous squamous cell carcinoma (SCC) and reduce recurrences.
It is estimated that 15-20% of AK lesions progress to CSCC, the second most common skin cancer in humans. This figure continues to rise, as the number of CECs has increased from 50% to 300% in the last three decades and by 2030 the incidence in European countries will be twice as high as it is today. Important indicators of individual risk of developing CSCC include immunosuppression, history of epithelial skin cancer, high cumulative UV exposure, number of lesions (> 5), gender (more common in men than women (3:1 ratio) and age (5-10 times higher in people over 75 compared to those under 55). Patients usually present with scaly, erythematous, ulcerated and/or bleeding lesions.
If detected and treated in early stages, CSCC is usually not life-threatening. However, it can be locally invasive (causing disfigurement) and metastatic. The frequency of lymph node metastases is around 4% and mortality rates are close to 3.5%. Given its high frequency, CSCC has a significant impact on overall mortality, being the second most common cause of death from skin cancer after melanoma.
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