Melanoma develops from cells called melanocytes. Melanocytes produce melanin, the substance that gives colour to the eyes, skin and hair. Intraocular melanoma is a cancer that develops from melanocytes in the eye. Because intraocular melanoma usually develops in the uvea part of the eye, it is also called uveal melanoma.
Intraocular melanoma and melanoma of the skin both develop from melanocytes, but they behave differently. For example, intraocular melanomas often spread to the liver first, whereas skin melanomas often spread to nearby lymph nodes. There are no lymphatic channels within the eye and orbit, so intraocular melanoma does not spread to nearby lymph nodes like melanoma of the skin. Intraocular melanomas spread to the liver when cancer cells enter the bloodstream and travel to the liver (which filters blood).
Intraocular melanoma accounts for about 5% of all melanomas. Although intraocular melanoma is rare, it is the most common type of primary cancer within the eye in adults. The incidence of intraocular melanoma increases with age. It is more common in people in their 60s and 70s and is slightly more common in men.
Intraocular melanomas can develop sporadically with no known cause (referred to as de novo) or develop from a pre-existing mole (nevusnevusSee mole.) in the eye.
Intraocular melanoma usually affects only one eye. There are 4 tissues in the eye area where melanoma can occur:
The uvea is the coloured (pigmented) layer that forms part of the wall of the eye. It lies between the sclera and the retina. The uvea is made up of the choroid, ciliary body and iris. Intraocular melanomas can develop anywhere in the uvea and can be classified as posterior or anterior uveal melanomas.
PosteriorPosteriorReferring to or having to do with the back of the body or a structure. uveal melanoma begins in the choroid or ciliary body further back in the eye.
AnteriorAnteriorReferring to or having to do with the front of the body or a structure. uveal melanoma begins in the iris near the front of the eye.
Uveal melanomas have distinct cell types within the tumour. These cancer cells are classified based on their size, shape and characteristics. The cell types found in intraocular melanoma are:
Mixed and epithelioid cell types are more common and more aggressive than spindle cell types.
Uveal melanoma often grows in the shape of a dome or a nodule (a small lump or growth made up of cells or tissues). Occasionally, the tumours are flat or spread out and involve extensive areas of the uvea. The size of the tumour is used to help classify and stage the melanoma and predict the chance of metastatic disease.
I’m extremely grateful to the Canadian Cancer Society for funding my research with an Innovation Grant.
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