Contributor: Gordon K. Klintworth
The melanoma is a common malignant neoplasm that may arise from normal melanocytes or from a preexisting lesion in different tissues, such as primary acquired conjunctival melanosis, nevocellular nevus [nevus - nevocellular] (especially junctional nevus [nevus - junctional]. The most frequent primary site is the skin [melanoma - skin], but this neoplasm occasionally arises in any part of the uvea [melanoma - uvea]. A primary melanoma can occur in the iris [melanoma - iris], ciliary body [melanoma - ciliary body] or choroid [melanoma - choroid].  A melanoma may also arise in the conjunctiva [melanoma - conjunctiva], eyelid [melanoma - eyelid] and even the orbit [melanoma - orbit]. An ocular melanoma may even be metastatic [melanoma - metastatic]. The intraocular lesion may extend directly into the anterior chamber from the iris or ciliary body. After invading through the retina a choroidal melanoma may disseminate to the anterior chamber. When a uveal melanoma undergoes extrensive necrosis [melanoma - necrotic] the necrotic debris can drain into the anterior chamber, where some of it may become phagocytosed by macrophages. The necrotic material and the associated macrophages can cause a black hyphema and this material may obstruct the drainage of aqueous humor from the eye leading to a specific type of secondary open angle glaucoma [glaucoma - secondary open angle] known as melanomalytic glaucoma [glaucoma - melanomalytic]. Excessive sun exposure is a risk factor for cutaneous melanoma. The biological behavior of metastatic melanoma is unpredictable.  Excessive sun exposure is a risk factor for cutaneous melanoma and most metastatic melanomas have their primary tumor in the skin.

A small cell malignant melanoma (House et al. J. Am Acad Dermatol 31:839-842, 1994) needs to be differentiated from othe small blue cell tumors (blue cell tumor).