Photodynamic diagnosis of pleural malignant lesions with a combination of 5-aminolevulinic acid and intrinsic fluorescence observation systems

Background: We have developed a new diagnostic method using the photosensitizer 5- aminolevulinic acid ( 5ALA) for diagnosing intrathoracic malignant lesions. When ingested exogenously, 5ALA is metabolized to a heme precursor, protoporphyrin IX, which stays in malignant cells and emits red to pink luminescence of about 630 nm. Methods: We enrolled 40 patients who underwent respiratory surgery and consented to participate in this study. Twenty- eight patients had primary lung cancer, 8 metastatic lung tumors, 2 malignant pleural tumors, and 2 benign tumors. Localization of malignant lesions was attempted by observing such lesions with an autofluorescence imaging system and by comparing the color tone of the autofluorescence between malignant lesions and normal tissues after oral administration of 5ALA. Malignant lesions on the pleural surface emitted pink autofluorescence in contrast to the green autofluorescence of the surrounding normal tissues. Results: When 28 patients with primary lung cancer were examined according to the degree of pleural infiltration ( pl), red fluorescence was confirmed in 10 of 10 patients ( 100%) with p11- p13 and 5 of 18 patients ( 27.7%) with p10. The latter 5 patients had been diagnosed with PL1 preoperatively or intraoperatively. Conclusion: This system achieved accurate localization of malignant lesions, suggesting that it may also be applicable to photodynamic therapy.