[Ultrastructure of transitional cell papillomas of the bladder]

Electron microscopy study of 18 transitional-cell papillomas of human bladder established the predominance of differentiated tumor cells exhibiting the ultrastructural features of superficial or intermediate cells of urothelium. Undifferentiated basal and squamous-epithelial tumor cells were less frequent. The ratio of cells at different stages of differentiation in papillomas of similar histological structure may vary. Application of electron microscopy offers practical advantage since it provides a means of objective assessment of the stage of tumor cell differentiation.