Effect of photodynamic therapy on a heterotransplanted human parotid tumor

To evaluate the effect of photodynamic therapy on human parotid tumors we used tumor specimens obtained from parotid surgery on a consecutive group of patients. The tumors were transplanted into a subcutaneous pocket of nude mice. The original human tumors were pleomorphic adenoma (four), adenolymphoma (one), acinic cell carcinoma (one), sarcoma (one) and low-grade adenocarcinoma (one). The most aggressive growth was seen in the low-grade adenocarcinoma. We re-implanted this tumor on ten mice bilaterally, and treated the tumors with photodynamic therapy (PDT), resulting in a mean depth of tumor necrosis of 5.4 mm (1-10 mm). In three cases we found vital tumor cells in the periphery of the tumor after treatment, with several new blood vessels in the surrounding tissue, indicating a great potential for neo-angiogenesis in this tumor. In order to evaluate the possible nerve damage subsequent to the photodynamic therapy, the ischiadic nerve in 24 lower limbs of nude mice were investigated. In one case only the macroscopical and histological investigation revealed signs of nerve damage. The current study demonstrates that the nude mice implantation model is excellent to investigate growth in both malignant and benign parotid tumors, and to test new therapeutic modalities. Photodynamic therapy seems to have a possible role in the future management of the malignant lesions of the parotid gland, in cases where radical surgery for some reason is not achievable.