Cytoskeletal intermediate filaments (IFs) constitute a diverse group of proteins that are expressed in a highly tissue-specific manner. Intermediate filaments are constructed from two-chain alpha-helical coiled-coil molecules arranged on an imperfect helical lattice and have been widely used as markers for distinguishing individual cell types within a tissue and identifying the origins of metastatic tumors. One such intermediate filament protein, Vimentin, is a general marker of cells originating in the mesenchyme. Vimentin is frequently co-expressed with other members of the intermediate filament family such as the cytokeratins,in neoplasms including melanoma and breast carcinoma. Vimentin and Desmin, a related class III intermediate filament, are both expressed during skeletal muscle development.