Most uveal melanomas occur in the choroid. The ciliary body is less commonly the site of origin and the iris the least common. Melanomas of the iris, which are often of the spindle A variety, are relatively slow growing and relatively benign. The major routes of spread are local extension and by the blood stream. The uveal tract is a vascular structure without lymphatic channels.
Systemic metastases are generally hematogenous in origin, and the liver is the most common site.
Lung and subcutaneous sites are common as well. In approximately two-thirds of the patients, the liver is the only site of detectable metastasis. In patients with a history of ocular melanoma who present with hepatic metastases of unknown origin, metastatic melanoma should be considered in the differential diagnosis. New radiolabeled monoclonal antibody scans may facilitate detection of extraocular disease, however, these scans are not yet universally available. Other techniques, such as ultrasonography, should be used to provide more accurate measurements.