What Causes Cat Iris Melanoma?

Iris melanoma is cancer of the melanin-containing cells of the eye. Melanin is the brown pigment in your kitty's eyes, hair and skin. Melanocytoma is the less aggressive form. It's considered benign because it doesn't spread -- metastasize -- to other tissues. An eye affected by melanocytoma can continue to function for years without any significant loss of vision. Melanosarcoma is the malignant form, meaning it can spread to the cornea and surrounding tissues. Melanosarcoma also causes physical breakdown of the iris with attendant loss of vision. Both forms can cause glaucoma -- painful pressure from fluid buildup within the eyeball -- but melanosarcoma does this much faster.

Heavy pigmentation is one predisposing factor for iris melanoma in cats. Melanocytes are concentrated in the back portion of the iris, behind the cells that give your kitty's eyes their normal color. Dark colored cats have larger numbers of melanocytes everywhere, including the iris. These kitties are predisposed to iris melanoma simply because there are more melanin-producing cells, so the risk of having a mutated one is higher.

Some cats are genetically predisposed to developing cancer, including iris melanoma. Genetic predispositions include melanocytes that mutate at a higher than average rate, immune systems less efficient at removing mutated or damaged cells, and hormonal imbalances that increase the risk of cancer.

Damaged melanocytes can become cancerous. We know UV radiation from the sun can damage melanocytes and cause skin cancer in human beings and other animals. Whether this also applies to melanocytes in the eye hasn't yet been proven, but most ophthalmic veterinarians believe there is a relationship. Exposure to any environmental toxin that damages iris melanocytes may also put your pet at risk for eventually developing melanoma.