CD63, a protein found in lysosomal membranes and weighing 53kDa, belongs to the tetraspanin family of molecules; it is recognized as a platelet surface antigen that becomes apparent upon activation. The cytoplasm of various cell types, such as lymphoid, myeloid, endothelial cells, and most malignant melanomas, exhibits reactivity with Anti-CD63. For detecting malignant melanoma through immunohistochemistry, Anti-CD63 serves as a valuable marker.