[Actinic keratosis: when is a skin biopsy necessary?].

The diagnosis of actinic keratosis is generally established by clinical examination. However, actinic keratosis can progress into an invasive squamous cell carcinoma, therefore biopsy and histological examination may be needed. The risk of progression into an invasive carcinoma is not well established; it varies in the literature between 0.025% and 20% for a given lesion. Some clinical aspects suggest transformation into an invasive carcinoma; they include inflammation, induration, size > 1 cm, rapid enlargement of the lesion, bleeding or ulceration, and should prompt the clinician to perform a skin biopsy. In case of resistance after a well-driven treatment, a biopsy may be necessary. Finally, in cases of atypical clinical aspect, a biopsy may be useful in order to obtain a correct diagnosis.