Vimentin is an intermediate filament expressed mainly in mesenchymal tissue and in primitive (undifferentiated) non-mesenchymal cells. It is a Class III cytoplasmic filament that forms a dense cytoskeletal network that extends from the nucleus to the plasma membrane. Vimentin reorganization during mitosis is likely regulated via its multiple phosphorylation sites. Vimentin expression is also found in mesoderm derived epithelia. Immunohistochemistry (IHC) with anti-vimentin antibodies is often used to identify neoplasms of mesenchymal or mesodermal origin.