Immunohistochemical analysis of pigment cell tumors in two cyprinid species

Pigment cell tumors, also known as chromatophoromas, are cutaneous spindle cell neoplasms originating from pigment cells (chromatophores) in the dermis of teleosts, amphibians, and reptiles. Chromatophoromas share similar histologic morphology to other spindle cell tumors and are not always pigmented. Therefore, immunohistochemical analysis may be useful in distinguishing these neoplasms from tumors of other cellular origin when poorly pigmented. We performed 3 immunohistochemistry assays (PNL-2, melan A, and SOX10) on 8 cutaneous neoplasms from 8 teleosts diagnosed as chromatophoromas based on histologic morphology. Semiquantitative analysis of immunoreactivity was evaluated on each immunohistochemical assay using a 0–3 scale. PNL-2 exhibited mild-to-moderate (1 or 2) immunoreactivity in 7 of the cases, and resident chromatophores (internal control) were also immunoreactive in these cases. Melan A exhibited mild-to-moderate (1 or 2) immunoreactivity in 4 cases (and with resident chromatophores in these cases); SOX10 was not immunoreactive in any cases. Our results indicate that PNL-2 may be a useful marker in teleosts to distinguish tumors of chromatophore origin. Melan A could also be useful, but appears to be less sensitive, and SOX10 is likely not a useful marker for these neoplasms in teleosts.