Tapioca melanoma of the iris: a contribution to the fine structure and its significance.

A case of iris malignant melanoma, macroscopically classified as tapioca melanoma, was studied by electron microscopy. The tumor originated in the left eye of a patient, and a specimen was obtained during iridociclectomy. Two main types of cells were found: the differences between them concerned mainly the Golgi complex, mitochondria, RER and free ribosomes. The melanotic bodies, scantly represented, were carefully examined. The ultrastructural findings enabled us to classify these two types of cells as spindle subtype B and epithelioid types. A comparison of ultrastructural features observed in our case with those of other melanomas of the uveal tract and the skin allowed us further to stress the hypothesis of a nevoblastic origin of the tapioca tumor cells.