S-100 immunoreactivity in melanomas of two marsupials, a bird, and a reptile.

S-100 proteins are abundant in melanocytes of the skin; thus, S-100 immunoreactivity has been used as a diagnostic criterion for melanoma in humans and other placental mammals. We tested cutaneous melanomas of two marsupials, a bird, and a snake for S-100 immunoreactivity, using a polyclonal rabbit antibovine S-100 antibody. The tumor from a Tasmanian Pademelon (Thylogale billaridierii) was composed of large epithelioid cells, most of which had S-100-positive cytoplasm. In general, there were only scattered individual spindle-shaped S-100-positive cells or groups of cells in the primary mass from a Spotted-tailed Quoll (Dasyurus maculatus); S-100 staining was primarily nuclear. Cells comprising the melanomas of the Australian Cormorant (Phalacrocorax carbo) and the Death Adder (Acanthophis antarcticus) were S-100-negative, although peripheral nerve bundles in both were S-100-positive.