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Spontaneous Regressive Epitheliomas in the Japanese Newt, Cynops pyrrhogaster

Faculty of Medicine, Memorial University of Newfoundland, St. John's, Newfoundland, Canada, A1B 3V6 [C. J. P.], and First Department of Surgery [T. N., T. T.] and Second Department of Surgery [M. F.], Kyoto University School of Medicine, Sakyo-ku, Kyoto, Japan 606

Spontaneous tumors in urodele amphibians have been considered uncommon, and this resistance has sometimes been associated with the natural regenerative capacity of tissues in such species. This report describes spontaneous, nonpigmented, benign epitheliomas which were found in 44 of 1586 (2.8%) adult newts, Cynops pyrrhogaster, captured in central Japan. Both sexes were affected equally, usually with single tumors occurring at any epidermal site. Under laboratory conditions, these large tumors rapidly regressed or disappeared. Lesions were histologically noninvasive, hyperplastic epidermal reactions accompanied by loss of basal, subdermal melanocytes. Ultrastructurally, enlargement of intercellular spaces between tumor cells, increased pigment granules and membrane-bound cytoplasmic aggregates within the spaces, swollen rough endoplasmic reticula, degenerating pigment granules, and altered corneal cells were noted. Virus-like particles were observed in one tumor cell. Preliminary attempts failed to demonstrate transmissibility of the tumor, and no new cases arose under laboratory conditions. The cause of these tumors in the Japanese newt remains unknown, and it is suggested that if a viral agent is involved then other environmental cofactors (diet, temperature, or water constituents) are required for its expression.

¹ The work reported in this paper was undertaken during the tenure of an American Cancer Society—Eleanor Roosevelt—International Cancer Fellowship awarded by the International Union Against Cancer. To whom requests for reprints should be addressed.

Received 8/ 3/78. Accepted 2/21/79.