Hyperkeratotic papule, formed by central keratinous plug surrounded by proliferating, atypical epidermal invagination. Dysplastic epidermis shows changes corresponding to the well differentiated squamous carcinoma, but cytoplasm is usually more eosinophilic. Mitotic activity is usually high, especially in early lesions. Epithel shows focal necroses and neutrophilic or eosinophilic microabscesses. At the base of the lesion there is usually dense lymphocytic infiltrate, often with admixture of eosinophils. At periphery the tumor shows limited infiltrating behavior.