A light in multidrug resistance: photodynamic treatment of multidrug-resistant tumors.

The major drawback of cancer chemotherapy is the development of multidrug-resistant (MDR) tumor cells, which are cross-resistant to a broad range of structurally and functionally unrelated agents, making it difficult to treat these tumors. In the last decade, a number of authors have studied the effects of photodynamic therapy (PDT), a combination of visible light with photosensitizing agents, on MDR cells. The results, although still inconclusive, have raised the possibility of treating MDR tumors by PDT.