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 billardierii) 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 maculates); 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.