Skin

Evaluation of skin pathology specimens requires a wide range of diagnostic skills including an integration of dermatological clinical examination together with a systematic histopathologic evaluation of both reactive and neoplastic conditions. This chapter reflects the complex cellular composition of the skin. Neoplastic conditions are divided according to cell of origin in epidermal, adnexal, melanocytic, neural (including Merkel cell carcinoma), soft tissue, and hematolymphoid proliferations. Emphasis is given to common malignant conditions, but unusual and rare entities are included for adequate differential diagnosis. Benign skin tumors are also discussed, and, when pertinent, reactive inflammatory conditions are described-particularly those encountered in patients being treated for either cutaneous or extracutaneous malignancies. Awareness of clinical presentation is crucial for many dermatological inflammatory conditions; at the same time, careful selection and interpretation of immunohistochemical and molecular studies are required for an accurate pathological diagnosis of cutaneous tumors.