S100 is a nervous tissue specific soluble protein made in glial cells. Present in sweat glands chondrocytes and myoepithelial cells. Used to mark melanomas, some breast carcinomas and neural tumors. Staining pattern may be found as cytoplasmic, membranous or mixed through the areas of tumor. Usually cytoplasmic when present in normal tissues.

Short term (up to 7 days) store at 2-8 °C. Long term, aliquot and store at -20 °C. Avoid multiple freeze/thaw cycles.