Photosensitization of malignant tumors.

Photodynamic therapy is a new, experimental method of treating malignant tumors by utilizing the relatively selective retention of the photosensitizer (hematoporphyrin derivative or dihematoporphyrin ether) and its ability to elicit an efficient photodynamic reaction upon activation with penetrating viable light. Application of this therapy to tumors in the bronchus, bladder, skin, and several other sites has demonstrated both safety and efficacy, even in advanced cases. Eradication of early stage tumors in the bronchus and bladder has been demonstrated. Selective retention of the photosensitizers in tumors is apparently related to the relatively large size of the aggregates of these materials causing phagocytosis by reticuloendothelial cells as well as preventing rapid clearance from tumor interstitial fluid and subsequent uptake in lipophylic components of cells. Upon light activation, generally delivered from lasers via fiber optics, the sensitizers generate singlet oxygen, the apparent cytotoxic agent, causing both vascular damage and injury to tumor cells.