An ultrastructural study of human bladder cancer treated by photodynamic therapy

An electron microscopic study has been carried out biopsy material of transitional cell carcinoma of human bladder, taken before and after photodynamic therapy (PDT), from 14 patients. It has been demonstrated that bladder cancer is highly sensitive to PDT using haematoporphyrin derivative (HPD, made in China) and laser irradiation. It was found that vascular endothelium within the tumour tissue was very sensitive to PDT, showing distinct changes as early as immediately after completion of a 20-min irradiation. Twenty-four hours after PDT, almost all the capillaries examined were necrotic and broken down into small fragments. The cancer cells were less sensitive to PDT, being damaged later and less seriously than the blood vessels. It has been concluded that in PDT-treated tumours the vascular endothelium is damaged primarily while the cancer cells are destroyed, to a considerable extent, secondarily as the consequence of structural damage to capillaries and functional disturbance in the microcirculation. We would speculate that the main factor influencing the final response is the actual concentration of HPD in various types of cell in the tumours.