Melanoma, Intraocular (Eye)

WELL KNOWN TO the general public are cutaneous melanomas of the skin that involve malignant transformation of melanocytes—cells within the epidermis responsible for producing pigment. Melanomas can and do arise anywhere melanocytes exist in the body, however, including the eye. In fact, uveal melanoma is the most common primary intraocular malignancy in adults. The incidence of this tumor increases with age, reaching more than 20 million per year by the seventh decade of life. Although some experts have implicated excessive childhood exposure to ultraviolet radiation as a risk factor, this link is not nearly as clear as it is for cutaneous melanoma.

Human metastatic melanoma cells stained with an H & E stain and magnified to 320x.

The uvea includes the iris (the colored part of the eye that alters the amount of light entering the eye), the ciliary body (a muscle that changes the shape of the lens), and the choroid (a layer of tissue that lies next to the retina, which transmits visual information to the brain). Most melanomas of the iris, ciliary body, or choroid are initially completely asymptomatic, although iris melanomas may appear as a dark spot on the iris. As the tumor enlarges, it may cause distortion of the pupil (iris melanoma), blurred vision and glaucoma (ciliary body melanoma), or markedly decreased visual acuity from a secondary retinal detachment (choroidal melanoma). Most melanomas are detected by routine ophthalmic examinations with pupil dilation.

Melanomas situated exclusively in the iris tend to follow a relatively indolent course, whereas melanomas of the ciliary body and choroids are more aggressive. The prognosis of choroidal and ciliary body melanomas is classically related to size, cell type, and proliferative index. By contrast to cutaneous melanomas, large numbers of tumor-infiltrating lymphocytes are associated with an adverse outcome, as are extraocular extension, tumor involvement of the ciliary body, and advanced age of the patient.

When a definite diagnosis of malignant melanoma is made, possible therapies are selected depending on the location and size of the tumor. Small melanomas of the iris or ciliary body sometimes are successfully treated by iridectomy—removal of the part of the iris harboring the tumor. With very large tumors, the only possible option is enucleation, or removal of the eye, followed by placement of an artificial eye in the socket. Plaque therapy is a novel form of radiation therapy effective in treating malignant melanoma of the ciliary body or choroids. The technique involves the localized delivery of radiation to the tumor by a small metallic object containing radioisotopes, sutured to the wall of the eye adjacent to the base of the tumor. In certain situations, laser therapy is used to destroy the tumor with an intensely powerful beam of light. Photocoagulation can also be performed. This procedure uses the laser to destroy the blood vessels that feed the tumor, thus eliminating its nutrient source.

Despite the efficacy of many available therapies in achieving local tumor control, eventual death due to metastases (especially to the liver) may occur in up to 50 percent of patients. Although the 5-year survival [Page 575]rate is approximately 80 percent, the cumulative melanoma mortality rate is 40 percent at 10 years, increasing by 1 percent per year thereafter. Examples of metastases appearing many years after treatment are also well known.

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