Spontaneous uveal amelanotic melanoma in transgenic Tyr-RAS Ink4a/Arf-/- mice

Objective: To characterize a murine model of spontaneous amelanotic melanoma arising in the uvea of transgenic mice bearing a targeted deletion of the Ink4a/Arf tumor suppressor locus (exons 2 and 3) and expressing human H-ras controlled by the human tyrosinase promoter. Methods: Ocular lesions developed in 20 (15.7%) of 127 male albino Tyr-RAS+ Ink4a/Arf-/- transgenic FVB/N mice within 6 months, and were evaluated histologically and ultrastructurally. Results: Uveal melanomas were locally invasive but confined to the eye, with no evidence of metastasis. Tumor cells exhibited epithelioid and spindle-shaped morphological features and closely resembled the human counterpart. Melan-A, S100 and neuron-specific enolase expression were detected immunohistochemically. Melanosomal structures were detected using electron microscopy. The retinal pigment epithelium was intact above small melanomas, and electron microscopy of the tumors failed to show the presence of basement membrane formation or desmosomes. Conclusion: Spontaneous uveal malignant melanomas occurring in male Tyr-RAS+ Ink4a/Arf-/- transgenic mice arise within the choroid or ciliary body and share histopathological features characteristic of human uveal melanoma. Clinical Relevance: Uveal melanoma research has benefited from xenograft models, but engineered mouse models of spontaneous uveal amelanotic melanoma will undoubtedly further our understanding of the genetic underpinning for this disease.