(106) HMB-45 (anti-gp100), a premelanosome
marker, has been shown to mark the intraepidermal and superficial dermal components of melanocytic nevi, with the exception of diffuse dermal staining in blue nevi.
Similarly, Stone et al (16) detected HMB-45 and NK1-C3 immunoreactivity predominantly in epithelioid and spindle cells and premelanosome
-like structures in epithelioid cells in 9 cases by electron microscopy.
Dendritic, pigmented cells show positivity for Masson-Fontana stain; express S100 protein, Melan-A, and HMB-45; and contain premelanosomes
and mature melanosomes.
The electron microscopy study revealed the presence of cells containing electron-dense granules, whose ultrastructural features corresponded to premelanosomes
These LAM cells have partial melanocytic differentiation and stain positive for HMB-45 (a glycoprotein occurring in the premelanosomes
in the cytoplasm).
The HMB-45 marker, which identifies gpioo (glycoprotein of premelanosomes
), is considered more specific than the S-100 marker but it also does not show absolute specificity because it can be expressed in the cells of sweat glands and non-melanocytic tumors (24, 31, 32).
The second population exhibits fine elongations, enclosed in basal membrane while the third population consists of dendritic cells containing melanosomes and premelanosomes
The ink is a complex mixture of organelles, premelanosomes
, melanosomes, granules, proteic material (enzymes), glucosamine, and phospholipids in suspension.
(12) Electron microscopy may identify the presence of melanosomes or premelanosomes
. Although the tumor in our patient appeared to be amelanotic on clinical examination, melanin pigmentation was seen in the cytoplasm on microscopy, and immunohistology was positive for S-100 protein.
Markers such as chromogranin A and gp100 (the target of antibody HMB-45) localize to granular structures within the cell and tumor cytoplasm, in dense core granules (chromogranin A) and premelanosomes
No melanosomes or melanosome-like structures have been identified, although premelanosomes
were very occasionally seen in one case.
No intracytoplamic filaments, premelanosomes
, or intercellular junctions were identified.