Microscopic sections of the biopsy specimen from the right forearm revealed extensive acanthosis and focal superficial ulceration. There were prominent proliferating islands of atypical squamous epithelium, with multifocal subepithelial microabscesses. The tongues of squamous epithelium displayed mild to moderate dyskeratosis, horn pearls, pleomorphism, and rare mitotic figures.
Between the masses of atypical squamous epithelium, there were dense inflammatory infiltrates composed of large, hyperchromatic cells with extensive variability in size and shape. Many of the neoplastic cells exhibited prominent eosinophilic nuclei, abundant cytoplasm, and striking nuclear polymorphism. A surrounding infiltrate of small reactive lymphocytes, macrophages, and eosinophils was also noted.