Melanomas can arise in somewhat unusual locations, such as under the nail of a finger or toe or on the mucosa lining the inside of the mouth, vagina or anus. Primary melanomas have also been found on the pigmented tissue covering the brain (the meninges). It is important not to confuse melanomas under the nail with fungal infections, although that mistake is sometimes made at the beginning of the disease.
Melanomas of the eye occur in the colored regions at the front (the iris), just behind the iris in the structure controlling the shape of the lens (the ciliary body) and in the pigmented layer (the choroid) covering the eyeball behind the retina.
How It Spreads There are two phases of growth of melanomas—the radial (outward on the surface of the skin) and the vertical (deeply into the layers of the skin). Sometimes, superficial spreading melanomas can remain in a radial growth phase for over a year. Nodular melanomas grow vertically soon after their appearance. Detection in a biologically early phase is, therefore, more likely with superficial spreading melanomas, but these tumors do eventually enter a vertical growth phase. When they do, they are as dangerous as nodular melanomas.
Most eye melanomas grow very slowly. They may be observed by ophthalmologists for 5 to 10 years with little increase in size. The eye melanomas composed of spindle-shaped cells (called spindle A and spindle B) are almost non-malignant in their behavior, with almost all patients surviving more than 10 years after the tumor is detected. Other varieties, composed of cells shaped more like skin cells (epithelioid) are much more malignant .
