PMEL17 / GP100 is a melanocyte-specific type I transmembrane glycoprotein. It is enriched in melanosomes, which are the melanin-producing organelles in melanocytes, and plays an essential role in the structural organization of premelanosomes. PMEL17 / GP100 is involved in generating internal matrix fibers that define the transition from stage I to stage II melanosomes. PMEL17 expression is melanocytic-cell-lineage-restricted and with significant transcript levels in all stages of melanoma progression, including early and amelanotic melanoma lesions. The PMEL17 antibody specifically labels melanoma cells.