Incipient intraepidermal cutaneous squamous cell carcinoma: a proposal for reclassifying and grading solar (actinic) keratoses.

Actinic keratoses (AKs) are primarily induced by ultraviolet (UV) radiation and are often identified as premalignant lesions. In our opinion, AKs are proliferations of transformed, neoplastic keratinocytes confined to the epidermis that may eventually extend into the dermis, at which point they are termed squamous cell carcinoma (SCC). In contrast to AKs, SCCs have the potential to metastasize and kill. This process is analogous to that of evolving carcinoma of the uterine cervix that has been termed cervical intraepithelial neoplasia (CIN), a time-tested and reliable classification that provides clinicians with accurate information on which to base treatment decisions regarding cervical neoplasms following biopsy testing. A similar classification scheme could provide guidance to clinicians for the diagnosis and treatment of evolving SCC of the skin and as such, we propose a similar classification using the terminology keratinocytic intraepidermal neoplasia (KIN). This system is more reflective of the histology and natural history of SCC and eliminates ambiguity in the terminology of lesions currently referred to as AKs. The KIN classification defines features by which individual specimens can be objectively graded and specific treatment recommendations are made based on the grade of the lesion. We propose that the term keratinocytic intraepidermal neoplasia (KIN) be used to define and describe evolving SCC of the skin and that the term actinic (solar) keratosis be eliminated.