Induction of ocular tumor by nickel subsulfide in the Japanese common newt, Cynops pyrrhogaster.

Chemically induced ocular tumors in amphibians have not been reported previously. In the present study, nickel subsulfide (Ni3S2) was administered to lentectomized Japanese common newts, Cynops pyrrhogaster, by a single injection into the posterior chamber of the right eye (40-100 micrograms Ni3S2/newt). Control newts received a similar injection of vehicle. Malignant melanoma-like tumors developed in the injected eyes of seven of eight Ni3S2-treated newts at 9 months (versus none of six controls). Tumor cells occupied the entire globe and invaded the surrounding tissues. At 11 months melanoma-like cells in treated eyes exhibited by electron microscopy deeply invaginated nuclei and various degrees of pigmentation. Some cells even contained crystalline Ni3S2 in the cytoplasm at 11 months. Mitotic figures were rare in treated eyes at 9 months but were often found in them at 3 months. In one of the seven tumor-bearing eyes at 9 months, a prominent metaplastic cartilage was observed within the globe. A regenerated lens was noted at 9 months in a Ni3S2-treated eye which escaped tumor induction. The site of tumor origin was assumed to be the iris, because the aberrantly proliferating cell population was predominantly found in the root of the iris in treated eyes at 3 months.