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Tumor Classification System

Selected by the SciLinks program, a service of National Science Teachers Association. Copyright 2001.

Contributed by Irma Gimenez-Conti, Steven Kazianis, Rodney Nairn, Don Morizot, and Ron Walter

Kazianis, S., Gimenez-Conti, I., Trono, D., Pedroza, A., Chovanec, L., Morizot, D.C.,
Nairn, R.S., and R.B. Walter (2001) "Genetic Analysis of MNU-Induced Neoplasia
within Xiphophorus Hybrid Fish." Marine Biotechnology 3(S1): 37-44.


Melanotic Tumors


Melano-Macromelanophoro Polymorphic Melanoma

These tumors are very heterogeneous, with heavily and lightly pigmented areas. They are mixed tumors containing different cell types, including melanocytes, epithelioid-like cells, melanophores, and macromelanophore cells. Many also encompass groups of large fat-containing cells, especially those appearing ventrally on the body. Any one of these cells may constitute the predominant cell type; usually, different cell types predominate in different areas of the tumor.


Melanocytic Melanoma

These tumors are characterized histologically by a proliferation of melanocytes. These cells are dendritic in shape and contain variable amounts of pigment. These melanomas may invade and destroy the muscle bundles to different degrees.


Spindle-Cell Type Melanoma

These tumors contain spindle cells that extend into the dermis. Some tumors invade the muscles, while others were confined to the dermis. In the latter case, tumors may show different degrees of pigmentation.


Epithelioid-Cell Type Melanoma

These tumors are usually less heavily pigmented and formed by cells morphologically resembling epithelial cells. They are polyhedral cells with large nuclei and prominent nucleoli. These tumors are predominantly exophytic and appear to be less invasive into the muscle bundles than are the melanocytic and spindle cell type melanomas.


Amelanotic Melanoma

These tumors are defined by their gross appearance. Even though they appear macroscopically as non-pigmented lesions, microscopically they contain small areas with pigmented cells. They are commonly exophytic. Macroscopically, they appeared as hypopigmented, obviously exophytic growths that were bordered by melanistic regions. These neoplasms developed in the X. helleri x (X. maculatus Jp 163 B x X. helleri) cross, and arose after MNU treatment.

Neurological Tumors



Left, Photograph of a fish taken from above showing protrusion of the right eye. Center, Tumor cells invading the inner and outer surface of the retina, the sclera and the optic nerve. Right, Higher magnification photomicrograph showing tumor cell histological characteristics. The arrows delineate the area that shows a rosette-like arrangement. Scale bars are 200 mm.



Left, Example of a fish developing fibrosarcoma on the base of the caudal fin. Center, Low magnification image of a fibrosarcoma infiltrating muscular structure. Right, Muscle bundles compressed by whorled masses of densely packed spindle cells.



Left, Example of a fish developing fibrosarcoma on the base of the caudal fin. Center, Area of typical palisades. Right, A well circumscribed schwannoma.
MPNST Malignant Peripheral Nerve Sheath Tumor

MS Melanosis

Left, An MNU treated fish with a radially spreading melanosis that is not restricted to the gonopodial region. Right, Cross section of the anterior caudal peduncle showing pronounced melanosis within the integument with a lack of invasiveness. Scale bars are 200 mm.

Other Tumors


Renal Carcinoma