An Epithelioid Cell Type of Amelanotic Melanoma of the Pinna in a Fischer-344 Rat: A Case Report

Abstract

An epithelioid cell type of spontaneous amelanotic melanoma in the pinna of an aged albino Fischer-344 (F-344) rat is described. When the rat was necropsied at 109 wk of age, the pinnal tumor was recognized as a white spherical mass of 4 mm in diameter. Histologically, the tumor was observed in the dermis and composed of large round or polyhedral epithelioid eosinophilic cells that were arranged in various-sized cell nests. Immunohistochemistry demonstrated that the tumor cells were positive for S-100 protein and vimentin but negative for keratin and a rat macrophage antigen. Ultrastructurally, a few single membrane-bound premelanosomes that were accompanied by many primary lysosome-like bodies containing very fine granules were present in the cytoplasm of the tumor cells. This study has disclosed that, in addition to spindle cell variants of amelanotic melanomas, an epithelioid cell type of amelanotic melanoma may occur spontaneously in the skin of F-344 rats.

Keywords

Spontaneous tumor histopathology S-100 protein vimentin ultrastructure premelanosomes

References

Bomirski A. , Zawrocka-Wrzolkowa T. , and Pautsch F. (1973). Electron microscopic studies on transplantable melanotic and amelanotic melanomas in hamsters. Arch. Dermatol. Forsch. 46: 284-298.

Damoiseaux JG , Dopp EA , Calame W. , Chao D. , MacPherson GG , and Dijkstra CD (1994). Rat macrophage lysosomal membrane recognized by monoclonal antibody ED1. Immunology 83: 140-147.

Elder DE and Murphy GF (1991). Melanocytic Tumors of the Skin, Atlas of Tumor Pathology, 3rd ser., Fasc. 2. Armed Forces Institute of Pathology, Washington, D.C.

Nakashima N. , Mitsumori K. , Maita K. , and Shirasu Y. (1991). Amelanotic melanocytic tumors of the pinna in six F344 rats. J. Vet. Med. Sci. 53: 291-296.

Slominski A. , Moellmann G. , and Kuklinska E. (1989). L-tyrosine, L-DOPA, and tyrosinase as positive regulators of the subcellular apparatus of melanogenesis in Bomirski Ab amelanotic melanoma cells. Pigment Cell Res . 2: 109-116.

Yoshitomi K. and Boorman GA (1993). Palpebral amelanotic melanomas in F344 rats. Vet. Pathol. 30: 280-286.

Yoshitomi K. and Brown HR (1990). The ear and pinna. In: Pathology of Fischer Rat, GA Boorman , SL Eustis , MR Elwell , CA Montgomery , and WF MacKenzie (eds). Academic Press , New York, pp. 227-238.

Yoshitomi K. , Elwell MR , and Boorman GA (1995). Pathology and incidence of amelanotic melanomas of the skin in F-344/N rats . Toxicol. Pathol. 23: 16-25.

Zurcher C. and Roholl PJM (1989). Melanocytic tumors, rat. In: Monographs on Pathology of Laboratory Animals Sponsored by the International Life Sciences Institute: Integument and Mammary Glands, TC Jones, U Mohr , and RD Hunt (eds). Springer-Verlag, New York, pp. 76-86.