Choroidal malignant melanoma in an albino.

This is the first report of an amelanotic melanoma arising in the unpigmented choroid of a tyrosinase-positive oculocutaneous albino (TPOCA). Melanosomes within the tumour showed a maturation arrest in the unpigmented type II (premelanosome) phase. Other neural crest derived melanocytes in iris and choroid showed similar limited melanogenesis. The neuroectodermally derived melanocytes of the iris, ciliary body, and retinal pigment epithelium (RPE) contained mature melanosomes, though clinically the RPE was pale. The significance of this tumour arising in an albinotic eye is discussed.