S-100is structurally similar to calmodulin and gets its name from the fact that it is 100% soluble in ammonium sulfate at neutral pH. It is an acidic protein present in the cytoplasm and nucleus, so staining of both is usually required to call the stain positive. It is present in neural crest cells, making it a useful marker for melanoma, as well as chondrocytes, adipocytes, myoepithelial cells, macrophages, Langerhans cells, and dendritic cells.
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Also known as MART-1, for Melanocytic Antigen Recognized by cytotoxic T lymphocytes from melanoma patients, it is a sensitive and specific cytoplasmic protein for melanoma.
PAS stains glycogen as well as mucins, but tissue can be pre-digested with diastase to remove glycogen. It stains neutral and acid-simple non-sulfated and acid-complex sulfated mucins.
Mucicarmine contains carmine (red coloring material) and aluminum chloride and is very specific for epithelial mucins, including adenocarcinomas.
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