Skin, Actinic keratosis

Actinic keratosis is a cutaneous lesion on sun-exposed areas. It is a precursor lesion that can give rise to squamous cell carcinoma and is more often found in individuals with fair skin.

Microscopically, there is marked hyperkaratosis and basal cell layer atypia. Solar elastosis can also be seen in the papillary dermis. There is parakeratosis and the granular cell layer is diminished. There are many histologic variants such as hypertrophic, atrophic, acantholytic, lichenoid, etc. When the cytologic atypia reaches the full thickness of the epidermal layer, this is called Bowen's disease or squamous cell carcinoma in situ.