Canine Balloon and Signet-ring Cell Melanomas: a Histological and Immunohistochemical Characterization

Follicular Stem Cell Carcinoma: Histologic, Immunohistochemical, Ultrastructural, and Clinical Characterization in 30 Dogs

“…29 Finally, S100a was not expressed in follicular stem cell carcinomas, whereas it is expressed by a large proportion of canine melanomas. 4,29 Electron microscopy further confirmed a diagnosis of epithelial tumor and also differentiated follicular stem cell carcinomas from melanomas. Unlike follicular stem cell carcinomas, melanomas lack desmosomes, neuroendocrine-like granules, intercellular lumina, and intracellular ductules.…”

“…Cytokeratin was expressed in all but one follicular stem cell carcinomas, whereas it is not expressed in ca-nine melanomas. 4 Vimentin was expressed by a limited number of cells in follicular stem cell carcinomass, whereas it is generally expressed by all cells in melanomas. 29 Finally, S100a was not expressed in follicular stem cell carcinomas, whereas it is expressed by a large proportion of canine melanomas.…”

Cutaneous amelanotic signet-ring cell malignant melanoma with interspersed myofibroblastic differentiation in a young cat

“…12 Mixtures of signet-ring and epithelioid-type cells have been reported in dogs and cats. 8,25 Divergent differentiations as reported in human malignant melanomas such as fibroblastic or myofibroblastic, Schwannian and perineurial, smooth muscle, rhabdomyosarcomatous, osteocartilaginous, ganglionic and ganglioneuroblastic, neuroendocrine, and epithelial are not clearly distinguished as such in the WHO DA. 3,12 In our case, myofibroblastic differentiation as opposed to proliferation of reactive stromal myofibroblasts was supported by histologic features such as anisokaryosis and anisocytosis of these cells, the appearance of very plump spindle cells suggesting they may represent intermediate cells between signet-ring and spindle cells, and the overall irregularity in which spindle cells interweave between signet-ring cells that is not typical for stromal cells (Fig.…”

“…23,25 In addition to this report, signet-ring cell melanomas have been described only rarely in the skin of dogs and cats. 8,17,25 Electron microscopy revealed that the signet-ring cell morphology is caused by numerous aggregates of vimentin-positive intermediate filaments. 1,23,25 Comparable to previous canine and feline studies, the presented tumor was amelanotic, confirmed by negative Fontana staining, which made the diagnosis of melanoma even more difficult and strengthened the need for expression pattern analysis of the tumor cells.…”

“…1,23,25 Comparable to previous canine and feline studies, the presented tumor was amelanotic, confirmed by negative Fontana staining, which made the diagnosis of melanoma even more difficult and strengthened the need for expression pattern analysis of the tumor cells. 8,25 All feline and canine signet-ring cell melanomas reported to date were positive for vimentin, S100, and NSE; however, melan A was not tested or only present in 1 canine case. 8,25 Signet-ring cells of our tumor also constantly expressed vimentin (Fig.…”