A proposed classification scheme for Xiphophorus melanomas based on histopathologic analyses

We studied the histopathologic characteristics of melanomas induced in the Xiphophorus model. This fish model has been used for several decades to stu dy the molecular and genetic mechanisms underlying its susceptibility to me lanoma induction. Numerous distinct interspecific hybrid crosses currently are being used in research on carcinogenesis. We previously reported that t umors were induced in such hybrid crosses after treatment with N-methyl-N-n itrosourea or UV radiation. In this report, we describe the histopathologic features of Xiphophorus melanomas and propose a new classification system. We suggest that melanomas in these fishes can be classified as follows: me lanocytic melanomas; melanophorous-macromelanophorous polymorphic melanomas ; spindle cell type melanomas; epithelioid cell melanomas; and amelanotic m elanomas. The new classification of Xiphophorus melanomas should allow corr elations between histopathologic characteristics and carcinogen treatment, and between histopathologic characteristics and the genetic background of t he hybrid fish.