About Ocular Melanoma

Ocular melanoma is the most common primary cancer of the eye in adults. It is diagnosed in about 2,500 adults every year in the United States and occurs most often in lightly pigmented individuals with a median age of 55 years. However, it can occur in all races and at any age.

Called "OM" for short, ocular melanoma is a malignant tumor that can grow and spread to other parts of the body - this process, known as metastasis, is often fatal and occurs in about half of all cases. Although produced from the same cells in the body, called melanocytes, OM is different from skin (or cutaneous) melanoma and is not related to sun exposure. Ocular Melanoma is the second most common type of melanoma after cutaneous and represents about 5% of all melanomas.

Introduction to Ocular Melanoma

Perhaps you've heard of melanoma. It develops from the cells that produce the dark-colored pigment melanin, which is responsible for our skin's coloring. These cells, called melanocytes, are found in other places in our bodies, too: our hair, the lining of our internal organs, and our eyes. So while most melanomas do form on the skin, it is possible for a melanoma to form elsewhere. When it forms in the eye, it’s known as ocular melanoma or, more specifically, uveal melanoma.

OM is much rarer than skin melanoma and behaves quite differently. There are other types of eye cancers, but OM is the most common in adults and the most dangerous. It's a potentially lethal disease which many people die from, especially when it spreads to the liver, a complication in about half of people diagnosed with this disease.

No one knows for sure why OM tumors form but there is heightened prevalence amongst fair-skinned and blue-eyed individuals. Originally, excessive exposure to sunlight was thought to be a key risk factor but no study has proven a direct linkage to development of OM tumors.

The Basics of OM

Ocular melanoma (“OM” for short) is a cancer of the eye diagnosed in approximately 2,000-2,500 adults annually in the United States. In both the U.S. and Europe, this equates to about 5 - 7.5 cases per million people per year and, for people over 50 years old, the incidence rate increases to around 21 per million per year.

Similar to melanoma of the skin, OM is a little understood and silent killer. In the majority of cases, ocular melanoma develops slowly from the pigmented cells of the choroid (choroidal melanoma) but it also can develop from the pigmented cells of the iris and ciliary body. You may hear it called uveal melanoma because the uvea is a part of the eye containing two areas in which OM can commonly occur.

OM is an aggressive form of cancer that can involve any of three areas of the eye: the iris (the pigmented area surrounding your pupil), the ciliary body (a thin tissue layer in your eye responsible for aqueous humor production), and/or the choroid or posterior uvea (the vascular layer of the eye between the retina and the white outer layer known as the sclera; this pigmented tissue full of blood vessels nourishes the retina). These three areas are collectively known as the uvea or uveal tract, and OM can occur in any combination of the three. Iris melanomas have the best prognosis, whereas melanomas of the ciliary body have the worst. Most uveal tract melanomas originate in the choroid; the ciliary body is less commonly a site of origin, and the iris is the least common. Melanoma can also occur in the thin lining over the white part of the eye (the conjunctiva) or on the eyelid, but this is very rare.

OM tumors arise from the pigment cells (melanocytes) that give color to the eye. Formation of these tumors is quite rare and, as for many other forms of cancer, the exact cause is unknown. It is known that exposure to ultraviolet (UV) rays (either from the sun or sunbeds) increases the risk of developing melanoma of the skin. People whose skin burns easily are most at risk – people with fair skin, fair or red hair and blue eyes. However, there has no conclusive evidence linking UV exposure and OM.

Ocular melanoma may be more common in people who have atypical mole syndrome, which is also called dysplastic naevus syndrome. People with this condition have a greater risk of developing a melanoma of the skin, and often have over 100 moles on their body, some of which are abnormal in size and shape.

Approximately 2,500 adults are diagnosed with ocular melanoma every year. There is no known cause, though incidence is highest among people with lighter skin and blue eyes.

Approximately 50% of patients with OM will develop metastases by 10 to 15 years after diagnosis (a small percentage of people will develop metastases even later i.e. 20-25 years after their initial diagnosis). Metastatic disease is universally fatal. This 50% mortality rate is unchanged despite treatment advances in treating the primary eye tumor. More research is needed urgently to improve patient outcomes.