Pathological analysis. (A) Haematoxylin eosin stain shows clear nucleoli and some clear cytoplasm (arrow). (B) The mass is positive for HMB45 (human melanin black 45) (arrow). HMB45 is an antibody against the pre-melanosomal glycoprotein present in malignant melanoma and other tumours derived from melanocytes. (C) S100 is positive (arrow). It is an antibody against calcium-binding protein and is useful for staining nervous system tumours and malignant melanoma.