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Light and Electron Microscopic Studies of a Transplantable Melanoma Associated with Virus-like Particles¹

Department of Dermatology, University of California School of Medicine, San Francisco, California 94122

A transplantable melanoma of Golden hamsters has been carried by the chunk method from the 15th through the 52nd generation and examined for growth characteristics and for light and electron microscopic appearance as well as for light microscopy histochemistry. Grossly, tumors were heavily pigmented and invasive, and grew rapidly to kill the animals in 4 to 6 weeks. The growth rate remained stable within the 3 years of study. Histologically, malignant cells formed Fontanapositive pigment and grew as a solid tumor about dilated vascular channels with a supporting reticulum. Very little inflammatroy infiltrate occurred, but necrosis and hemorrhage were common. 3,4-Dihydroxy-L-phenylalanine oxidase and acid phosphatase activity were seen together in most viable cells. Ultrastructurally, in addition to premelanosomes and melanosomes, large polyribosomes and rough endoplasmic reticulum abounded in most cells. Large autophagic vacuoles containing melanin granules were seen frequently, suggesting that the cells did not discharge their melanin. Virus-like particles were observed in the rough endoplasmic reticulum in a majority of cells of every generation of tumor; they did not occur in inflammatory or endothelial cells, or in surrounding normal structures. Transplantation of the tumor in albino hamsters resulted in an identical pigmented tumor, except that it grew more slowly. Virus-like particles occurred in large amounts. The relationship of virus-like particles to melanoma formation remains unknown. They may transform cells to increase growth rate and account for the very rapid growth of heavily pigmented melanomas.

¹ This study was supported in part by a Cancer Research Coordinating Committee grant and in part by Research Evaluation and Allocation Committee Grant 26—Lartigau Fund, both from the University of California School of Medicine.

² Professor and Chairman, Department of Dermatology, University of California School of Medicine, San Francisco, Calif. To whom requests for reprints should be addressed, at the Department of Dermatology, 1096-HSE, University of California, San Francisco Medical Center, San Francisco, Calif. 94122.

³ Assistant Professor in Residence and Director, Dermatologic Research, Department of Dermatology, University of California School of Medicine, San Francisco, Calif.

Received 8/ 7/69. Accepted 11/ 5/69.