Nonmelanocytic

Nonmelanocytic is an adjective used in medicine to describe tissues, cells, or tumors that do not originate from melanocytes, the pigment-producing cells of the skin, eye, and certain other tissues. In dermatology and pathology, the term is used to distinguish lesions that arise from nonmelanocytic lineages from melanocytic lesions such as nevi and melanoma.

In clinical practice, nonmelanocytic lesions include most carcinomas and sarcomas of the skin as well as benign epidermal and adnexal lesions. They are contrasted with melanocytic lesions, which are defined by pigment-producing or melanocytic differentiation.

Examples of nonmelanocytic skin conditions include basal cell carcinoma, squamous cell carcinoma, seborrheic keratosis, keratoacanthoma, and Merkel cell carcinoma. Vascular and neural tumors of the skin, such as Kaposi sarcoma or schwannomas, are also nonmelanocytic.

Pathology relies on immunohistochemistry and lineage markers to distinguish nonmelanocytic from melanocytic lesions. Melanocytic markers such as S-100, Melan-A, and HMB-45 indicate melanocytic origin, whereas cytokeratins and other lineage markers point to nonmelanocytic tumors. Accurate classification informs prognosis and therapy.

See also: melanocytic lesion, melanoma, dermatopathology, histology.