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Diagnosing iris melanoma

Rushton JG, Ertl R, et al. Mutation analysis and gene expression profiling ocular melanomas in cats. Vet Comp Oncol. 2017 Jan 11. (Winn funded study)

In cats, the most common primary ocular tumor is diffuse iris melanoma. The only therapy currently for this malignant tumor is enucleation of the affected, often visual, eye. The reason this is necessary is because this type of melanoma may metastasize to the liver and lung in up to 60% of cases; also metastasis may occur up to 3 years post enucleation.

The diagnosis of diffuse iris melanoma can be challenging in the cat due to the similar appearance of benign iris melanosis, a common aging change in cats, and location (difficulty in obtaining a tissue biopsy). Also, areas of benign melanosis may undergo transformation at a later date into malignant melanoma. It is stated that little is known about the molecular biology of feline ocular melanomas.

In this study, the investigators look to determine whether feline ocular melanomas contain mutations comparable to mutations in human melanomas. They also want to evaluate the gene expression status of genes that are known to be involved in the initiation and progression of human melanomas. This is a step toward potentially diagnosing iris melanoma by a less invasive measure than the current practice of enucleation and tissue biopsy.

This study included by histopathologic results 10 cases of feline diffuse iris melanoma, 1 conjunctival melanoma and 1 uveal melanoma. The median age of the cats was 10 years; seven cats were female, four were male and one cat’s sex was listed unknown. The majority were domestic shorthaired cats and one was a Maine Coon.

The findings indicated that common mutations found in human melanomas were not found in these feline tumors. With gene expression analysis, there was significant upregulation of KIT and LTA4H, as well as down regulation of GNAQ, GNA11, BRAF and RASSF1 in the tumors. The authors state where KIT (KIT proto-oncogene receptor tyrosine kinase) appears to be a potential target gene in human melanomas, future research should look at the potential of KIT as a target for adjunctive therapy with this type of feline malignancy. (VT)

See also:
Van Raamsdonk CD, Griewank KG, et al. Mutations in GNA11 in uveal melanoma. N Engl J Med. 2010 Dec 2; 363(23):2191-2199.