Microscopic fluorescence in photodynamic therapy

The use of hematoporphyrin derivative (HPD) as a photosensitizer has been studied in malignant tumor detection via fluorescence and in tumor destruction via a toxic photochemical reaction. Squamous cell carcinoma has been induced in hamster buccal mucosa utilizing the known carcinogen dimethyl-benzanthracene. HPD was injected intraperitoneally, then at 24 and 48 hours following injection, unstained frozen section specimens were studied with fluorescent microscopy and photographed. The same specimens were then stained with hematoxylin and eosin and the microscopy correlated. HPD fluorescence was documented in the fibrous stroma of the tumor and in the keratin layer. Essentially no fluorescence was noted in the malignant squamous cells themselves. No consistent differences between the two postinjection times were noted. These qualitative observations support the postulated mechanism of HPD accumulation in tumors.