Basics of OM

"Uveal melanoma represents the most common primary intraocular malignancy in adults. Although
uveal and cutaneous melanomas both arise from melanocytes, uveal melanoma is clinically and biologically distinct from its more common cutaneous counterpart. Metastasis occurs frequently in this disease, and once distant spread occurs, outcomes are poor. No effective systemic therapies are currently available; however, recent advances in our understanding of the biology of this rare and devastating disease, combined with the growing availability of targeted agents, which can be used to rationally exploit these findings, hold the promise for novel and effective therapies in the foreseeable future."
 -  Therapeutic implications of the emerging molecular biology of uveal melanoma (2011)
    Patel M, Smyth E, Chapman PB, Wolchok JD, Schwartz GK, Abramson DH, Carvajal RD

Overview

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.

Anatomy of the Eye

Incidence

Ocular melanoma (“OM” for short) is a cancer of the eye diagnosed in approximately 2,000 adults annually in the United States. This equates to about 5 - 6 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.

Where Does It Come From?

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 – people with fair skin, fair or red hair and blue eyes -- are most at risk, thus doctors recommend regular, yearly check-ins with an experienced ophthalmologist. However, there has been 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.

How Serious Is It?

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.