Vessels of Intraocular Malignant Melanomas

: The vessel walls of six malignant choroidal melanomas were thin; only thin basal membranes and narrow endothelial linings could be observed with the electron microscope. The endothelium was even absent in some places. Tumor cells were released into the bloodstream through disruptions of the vessel walls in the epithelioid and spindle cell B type tumors.