Clinical features of actinic keratoses and early squamous cell carcinoma.

Clinically, there is a continuum between actinic keratosis, intraepidermal carcinoma (also known as squamous cell carcinoma in situ) and early squamous cell carcinoma that makes a reliable distinction between these entities extremely difficult. Each of the lesions in this continuum can be quite variable in clinical appearance, and there are often no clear distinguishing features, making it difficult to determine whether an individual actinic keratosis has evolved into intraepidermal carcinoma or invasive squamous cell carcinoma.