Figure 21.

Metachromasia of melanin by methyl green counterstaining in heavily pigmented nasal malignant melanoma (a) immunostaining for HMB45 and Berlin blue counterstaining for hemosiderin in pancreatic hemochromatosis (b) immunostaining for insulin. Brown-colored pigments such as melanin and hemosiderin hamper the judgment of DAB coloration. Counterstaining with methyl green and Berlin blue is quite effective for distinguishing the DAB color from the endogenous pigments. The rich distribution of HMB45-negative metachromatic melanophages is noted in panel (a). Arrows indicate HMB45-positive melanoma cells. In panel (b), hemosiderin deposition is observed in insulin-positive β-cells of the pancreatic islet (arrowheads).