Carcinoma in situ:
Carcinoma in situ is the histologic term used to describe cytologic evidence of malignancy (e.g. marked dysplasia, hyperchromasia, pleomorphism) confined to the epithelium with no invasion of underlying connective tissue or distant metastasis.
It shows extensive or patchy parakeratosis, hyperkeratosis, papillomatosis with broad epidermal papillae, thinning of the granular layer.
A chronic inflammatory cell infiltrate in the subjacent dermis is characteristic.
Variants include Bowen's disease ; Eryhtroplasia of Queyrat and Bowenoid papulosis.