Photodynamic therapy blocks spread of cancer
Helsinki – Using laser light to destroy tumour cells lodged in lymphatic vessels can halt the spread of cancer, Finnish researchers headed by Tuomas Tammela have demonstrated. Their approach to destroy the tumour cells, which use the tumour-associated vessels as a kind of motorway to spread around the whole body, with help of photodynamic therapy (Science Translational Medicine, DOI: 10.1126/scitranslmed.3001699), opens the door to fight the formation of metastases, which cause 90% of cancer deaths. To test their hypothesis that destruction of tumour-cells on their journey to the lymph nodes can reduce recurrence of cancer after removal of primary tumours the Finnish researchers made use of the light-activated cytotoxic pro-drug verteporfin, which is already marketed by Swiss Novartis AG to eliminate abnormal blood vessels that form in the course of wet macular degeneration. In mice, in which the researcher had induced the formatation of a primary tumor, treatment with the pro-drug and its subsequent activation through an infrared laser reduced the rate of cancer relapse from 65 percent to 10 percent. In a pig model, Tammela et al. showed that the drug acts as a blocker of lymphangiogenesis, the formation of new tumour associated lymphatic vessels. Pig’s lymphatic vessels became fragmented and clogged after treatment with the drug, hinting that photodynamic therapy may be able to destroy lymphatic vessels and also eradicate intralymphatic tumor cells nestled deep within tissues of human cancer patients. Up to now, treatment practice has not paid too much attention to residual tumour cells in metastatic transit inside the lymphatic vessels. The new findings may chance that.