Uveal melanoma is a type of eye cancer in the uvea of the eye. It is traditionally classed as originating in the iris, choroid, and ciliary body, but can also be divided into class I (low metastatic risk) and class II (high metastatic risk). Symptoms include blurred vision, loss of vision, and photopsia, but there may be no symptoms. Tumors arise from the pigment cells that reside within the uvea and give color to the eye. These melanocytes are distinct from the retinal pigment epithelium cells underlying the retina that do not form melanomas. When eye melanoma is spread to distant parts of the body, the five-year survival rate is about 15%. It is the most common type of primary eye cancer. Males and females are affected equally. More than 50% spread, mostly to the liver.
Types Uveal melanomas, often referred to by the media and in the general population as ocular melanomas, may arise from any of the three parts of the uvea, and are sometimes referred to by their location, choroidal melanoma, ciliary body melanoma, or iris melanoma. Large tumors often encompass multiple parts of the uvea and can be named accordingly. True iris melanomas, originating from within the iris as opposed to originating elsewhere and invading the iris, are distinct in their etiology and prognosis, such that the other tumors are often referred to collectively as posterior uveal melanomas.
Iris melanoma Uveal tumors can originate from melanocytes residing within the iris. Benign melanocytic tumors, such as iris freckles and moles (nevi), are common and pose no health risks, unless they show signs of malignancy, in which case they are classified as iris melanomas. Though derived from uveal melanocytes, iris melanomas share more in common with cutaneous (skin) melanomas in that they frequently harbor BRAF mutations associated with ultraviolet damage. Iris melanomas are much less likely to metastasize than other uveal melanomas, and less likely to impair vision if detected and treated early. Approximately 5% of uveal melanomas involve the iris.
Posterior uveal melanoma
Benign melanocytic tumors of the choroid, such as choroidal freckles and nevi, are very common and pose no health risks, unless they show signs of malignancy, in which case they are considered melanomas. Uveal melanoma is distinct from most skin melanomas associated with ultraviolet exposure; however, it shares several similarities with non-sun-exposed melanomas, such as acral melanomas and mucosal melanomas. BRAF mutations are extremely rare in posterior uveal melanomas; instead, uveal melanomas frequently harbor GNAQ/GNA11 mutations, a trait shared with blue nevi, nevus of Ota, and ocular melanosis. As seen in BRAF, mutations in GNAQ/GNA11 are early events in tumorigenesis and are not prognostic for tumor stage or later metastatic spread. In contrast, mutations in the gene BAP1 are strongly linked to metastatic spread and patient survival. Incidence of posterior uveal melanoma is highest among people with light skin and blue eyes. Other risk factors, such as blue light exposure and arc welding, have been put forward, but are still debated in the field. Mobile phone use is not a risk factor for uveal melanoma.
Signs and symptoms Ocular melanoma may present without symptoms depending upon the location and size of the tumor. When symptoms do occur, they can include:
blurred vision double vision (diplopia) irritation pain a perception of flashes of light in the eye (photopsia) a reduction in the total field of vision loss of vision a sensation of a foreign body in the field of vision (floaters) redness, bulging or displacement of the eye (proptosis) a change in the shape of the pupil pressure within the eye metamorphopsia (a distortion of vision where, when a person looks at a grid of straight lines, the lines appear wavy and parts of the grid appears blank).
Cause The cause of uveal melanoma is unclear. Uveal nevi are common (5% of Caucasians), but rarely progress to melanoma.
Metastasis Because there are no lymphatic channels to the uveal tract, metastasis occurs through local extension and/or blood-borne dissemination. The most common site of metastasis for uveal melanoma is the liver; the liver is the first site of metastasis for 80%-90% of ocular melanoma patients. Other common sites of metastasis include the lung, bones, and just beneath the skin (subcutaneous). Approximately 50 percent of patients will develop metastases within 15 years after treatment of the primary tumor, and the liver will be involved 90% of the time. Metastasis can occur more than 10 years after treatment of the primary tumor, and patients should not be considered cured even after a 10-year interval of monitoring. Molecular features of the tumor, including chromosome 3 status, chromosome 6p status, and chromosome 8q status and gene expression profiling (such as the DecisionDx-UM test), can be used to adjust this likelihood of metastasis for an individual patient. The average survival time after diagnosis of liver metastases depends on the extent of systemic spread. The disease-free interval, the performance status, the liver substitution by metastases and the serum level of lactic dehydrogenase are the most important prognostic factors for metastatic uveal melanoma. There is currently no cure for metastatic uveal melanoma.
Diagnosis
Treatment The treatment protocol for uveal melanoma has been directed by many clinical studies, the most important being The Collaborative Ocular Melanoma Study (COMS). The treatment varies depending upon many factors, chief among them the size of the tumor and results from testing of biopsied material from the tumor. Primary treatment can involve removal of the affected eye (enucleation); however, this is now reserved for cases of extreme tumor burden or other secondary problems. Advances in radiation therapies have significantly decreased the number of patients treated by enucleation in developed countries.
Plaque brachytherapy The most common radiation treatment is plaque brachytherapy, in which a small disc-shaped shield (plaque) encasing radioactive seeds (most often iodine-125, though ruthenium-106 and palladium-103 are also used) is attached to the outside surface of the eye, overlying the tumor. The plaque is left in place for a few days and then removed. The risk of metastasis after plaque radiotherapy is the same as that of enucleation, suggesting that micrometastatic spread occurs prior to treatment of the primary tumor.
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