Malignant melanoma of the choroid as related to coexistent benign nevus.

Ninety-five cases of malignant choroidal melanoma collected during a 15-year period have been studied with special emphasis on histological type, coexistence of benign nevus, and prognosis. Elements of benign nevus were found in 78% of the cases. The data tend to support the hyposis that most cases of malignant choroidal melanoma have their origin in a preexisting benign nevus, and that the tumours undergo a gradual change from a differentiated to a less differentiated type.