ABSTRACT
Definition: Commonly referred to as nonmelanocytic skin neoplasms, these are a large group of benign hyperplastic and malignant neoplasms arising from the epidermis.
General concepts • Most benign tumors have a well-circumscribed
silhouette characterized by epidermal hyperplasia (acanthosis, papillomatosis) and inconspicuous keratinocytes with preserved intercellular bridges, low nuclear/cytoplasmic ratio, and no atypia. – Clonal pattern: intraepidermal “nests of clonal
keratinocytes” (intraepidermal epithelioma or Borst-Jadassohn phenomenon) in seborrheic keratosis, large cell acanthoma, basal cell carcinoma and squamous cell carcinoma. It has recently been shown that the clonal keratinocytes strongly express epidermal growth factor receptor (EGF-R)
– Squamous eddies: whorled epithelial formations of glassy eosinophilic keratinocytes (inflamed seborrheic keratosis, inverted follicular keratosis)
• Most malignant tumors are characterized by epidermal hyperplasia or/and epidermal atrophy and atypical and pleomorphic keratinocytes with increased nuclear/cytoplasmic ratio, necrotic keratinocytes, and an increased number of atypical (asymmetric or multipolar) mitoses; in invasive carcinomas the atypical keratinocytes infiltrate the dermis, subdermis and their adjacent structures with potential for metastasis.
