Histopathology of melanocytic lesions in goats and establishment of a melanoma cell line: a potential model for human melanoma.

Melanocytic cells from white Angora goats were studied in vivo and in vitro. The histopathology of pigmented areas of skin from the most common sites of melanoma (solar-exposed areas of the ear, face, and perineum) resembled that of the epidermal melanocytes in Hutchinson's melanotic freckle in humans. Seven melanoma biopsies from 6 Angora goats showed histopathological features in common with human melanoma. A melanoma cell line, GM-1, was established in culture from a lymph node metastasis obtained from an animal that had a primary tumor excised and later developed extensive metastatic disease. GM-1 cells were mainly diploid, amelanotic, proliferated rapidly, spontaneously formed vacuolated cells, and were tumorigenic in nude mice. The species of origin of the GM-1 line was confirmed by isozyme profiles. GM-1 cultured cells and the original biopsy both expressed S-100 protein and tyrosinase antigen. Using GM-1 cells as the immunogen, a monoclonal antibody (MoAb 1F1) was derived that reacted strongly with a 116 kDa antigen in 50% of the GM-1 cells, but had little activity with goat fibroblasts (GM-F) or with human melanoma cells. GM-F, on the other hand, yielded more intense staining than GM-1 with an intermediate filament antibody (IFA), reacting with a 58 kDa antigen in both cell lines. The sensitivity of GM-1 to anticancer agents was similar to that of human melanoma cells. The pathology of caprine melanoma and its association with sun-exposed sites in relatively young animals suggest that it may be a suitable model for studying induction of melanoma by natural sunlight.