Iris melanoma.

The iris is the least common site of primary uveal melanoma. The prognosis of iris melanoma is better than that of melanoma of the ciliary body and choroid, but the reason for this difference is unclear. One possible explanation is that iris melanoma is smaller than its posterior segment counterparts at the time of diagnosis. Most iris melanomas are spindle cell types, according to a modified Callender classification system. There is evidence that the proliferation of melanocytes of the anterior iris surface (iris plaque) and diffuse stromal invasion may be risk factors for local recurrence and metastasis, respectively.