CD63 and neoplasm: Figures 2A and B illustrate the microvesicular urine fraction of the healthy donor. Two types of typical 500 nm-sized prostasomes are seen – ‘dark’ prostasomes with electron-dense contents and inclusions, and ‘light’, less dense ones. They were CD63 negative after immunogold staining (not shown). In contrast, microvesicles with cup-shaped morphology and size of 30–100 nm, typical for exosomes, were shown in the microvesicular urine fraction from the high-grade tumour (Figure 2C). Their exosomal nature was confirmed by immunoelectron microscopy after anti-CD63 gold staining (Figure 2D).