nonepithelial

Nonepithelial is a biological term used to describe cells, tissues, or tumors that are not of epithelial origin or not composed of epithelial cells. Epithelial tissue forms coverings, linings, and glands throughout the body; nonepithelial tissues comprise all other tissue types.

Major nonepithelial tissues include connective tissues (such as bone, cartilage, adipose tissue, blood, and tendons), muscle tissues (skeletal, smooth, and cardiac), and nervous tissue (neurons and glia). Blood is classed as a connective tissue despite its liquid form. These tissues typically have different cellular architectures and extracellular components compared with epithelia, reflecting their varied functions and developmental origins.

In pathology, nonepithelial describes tumors and lesions that arise from non-epithelial origins. Nonepithelial tumors are traditionally called sarcomas when they arise from mesenchymal tissues (for example fibrosarcoma or osteosarcoma) and include hematologic malignancies such as leukemias and lymphomas. By contrast, carcinomas are tumors of epithelial origin. Immunohistochemistry aids classification by detecting lineage-associated markers: cytokeratins identify epithelial cells, while vimentin supports a mesenchymal origin; neural or glial markers may indicate neural crest or central nervous system derivation.

Usage of the term is mainly descriptive in histology and pathology. It helps distinguish tissue and tumor origins for diagnostic, prognostic, and treatment considerations, particularly when assigning lineage and guiding marker-based testing.