S-100 is a soluble acidic protein. There are three subtypes, namely s-100ao, s-100a and s-100b. S-100 mainly exists in nervous tissue, pituitary, carotid body, adrenal medulla, salivary glands, and few interlobular tissues, S-100 is mainly used to diagnose the astrocytoma oligodendroglioma, ependymoma, neuroblastoma, schwannoma, malignant melanoma and liposarcoma.