Pathology and Incidence of Amelanotic Melanomas of the Skin in F-344/N Rats

Abstract

A total of 121 spontaneous amelanotic melanomas of the skin were identified in 70 of 11,171

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

“…The spontaneous amelanotic melanomas that have been reported in F-344 rats occur most commonly in the pinna (4,(6)(7)(8), as in the present case. However, they are composed predominantly of spindle-shaped cells that are arranged in interlacing bundles (4,(6)(7)(8).…”

“…These predilection sites of the tumor development are identical to those of melanotic melanomas in hooded rats (8). All of the cutaneous amelanotic melanomas that have been reported in F-344 rats are found in the dermis and composed primarily of spindleshaped cells.…”

“…They have close histologic similarities in cell morphology and proliferation pattern to Schwannomas or neurofibromas (4,6,7). Ultrastructurally, many intracytoplasmic premelanosomes (a precursor body of the melanin granule) are present in the spindle amelanotic melanoma cells (4,(6)(7)(8). To (Figs.…”

“…A few recent reports have demonstrated spontaneous amelanotic melanomas occurring in the pinna, eyelid, scrotum, or perianal/tail regions of albino Fischer-344 (F-344) rats (4,(6)(7)(8). These predilection sites of the tumor development are identical to those of melanotic melanomas in hooded rats (8).…”

“…However, they are composed predominantly of spindle-shaped cells that are arranged in interlacing bundles (4,(6)(7)(8). In the spindle cell type of melanoma in F-344 rats, epithelioid cells have been detected only as a rare solitary component (4,6,8), although a type of melanoma in pigmented rats has been reported to have areas of epithelioid cell growth (9).…”