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  • Precursor lesions of cutaneous squamous cell carcinoma (SCC).

  • Long-term and cumulative ultraviolet (UV) radiation exposure is the most important etiologic factor in the development of actinic keratoses.

  • Risk factors include fair skin, age, cumulative UV radiation exposure, immunosuppression, prior history of non-melanoma skin cancer.

  • The overall risk of progression to invasive SCC is estimated as 5% to 10%.

  • Treatment is recommended to reduce the risk of SCC formation and to improve patients’ quality of life.

  • Treatment modalities include cryosurgery, shave excision, curettage, dermabrasion, ablative lasers, topical drugs (diclofenac + hyaluronic acid, 5-fluorouracil ± salicylic acid, imiquimod, ingenol mebutate), chemical peelings, and photodynamic therapy.

Actinic keratoses (AKs, also known as solar keratoses or senile keratoses) are cutaneous lesions that consist of proliferations of atypical epidermal keratinocytes that may progress to invasive squamous cell carcinoma (SCC). The concept of a precancerous keratosis was first presented by Dubreuilh in the late 1800s. AKs were first identified and named keratoma senilis by Freudenthal in 1926. In 1958, Pinkus further characterized these lesions and coined the term actinic keratosis. It literally means a condition (-osis) of excessive horny (kerat-) tissue induced by a ray of light (aktis), presumably ultraviolet (UV) light. AKs have historically been considered precancerous or premalignant lesions with a potential for developing into SCCs. However, there is a debate at what grade of atypia AKs should be considered carcinoma in situ because not all AKs progress to SCCs and some lesions may spontaneously regress. Attempts have been made to coin AK as “keratinocytic intraepidermal neoplasia” grades I to III according to the degree of atypia.1 This concept is analogous to the grading of other precancerous lesions such as the classification of cervical intraepithelial neoplasia or vulvar intraepithelial neoplasia (VIN) as precursor lesions of cervical and vulvar carcinoma, respectively.

Regardless of the clinical course of single lesions, AKs are a strong indicator of chronic exposure to UV radiation with actinic skin damage and identify patients who are at high risk to develop nonmelanoma skin cancer. In an increasingly aging society with generations that poorly used sun protection measures and sunscreen, AKs are nowadays rated among the most common reasons to consult a dermatologist in regions with predominantly white populations such as the United States, Australia, and Europe.2 The high prevalence and the uncertainty of the clinical course of the precancerous lesions make AKs an important challenge for patients and physicians, and an economic burden for health-care providers.


In European countries, such as Spain and Austria, the prevalence of AKs in adult dermatology outpatients was reported to be approximately 30% in 2011. In the Netherlands, a total of 23.5% of the general population older than 50 years of age was estimated to be affected in 2011.3 Similar numbers were reported in the United States, where AK is the ...

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