PMEL and schwannoma: This special nerve sheath tumor strongly expressed S-100, leu-7, HMB-45, and vimentin, whereas GFAP, EMA, and CK staining were mostly negative.[8,9] In contrast to the typical encapsulation of conventional schwannoma, MS is a circumscribed but unencapsulated tumor, which may reflect the potential of a more aggressive nature such as an invasive growth pattern.