"S100 is a family of cytoplasmic calcium-binding proteins expressed in numerous cell lines which can be targeted by immunohistochemistry. Staining for S100 is helpful in characterising a number of tumours, including malignant melanoma, glial tumours, neurogenic tumours (e.g. schwannomas and neurofibromas), mesenchymal tumours (e.g. chondromas, chondrosarcomas, liposarcomas, some osteogenic sarcomas) and some histiocytic tumours 1,2."