The Biology of Glioma—A Discussion from the Standpoint of Photodynamic Diagnosis and Photodynamic Therapy

Abstract

Various treatment modalities for malignant glioma have not markedly prolonged the survival of patients. However, maximal surgical resection of the tumor has been shown to be an effective means of dealing with this malignancy. Surgery is therefore an important first step of treatment which determines the prognosis of patients with malignant glioma. Various methods have been developed for preoperative and intraoperative evaluation of the function of surrounding areas of the brain and intraoperative identification of the tumor. Fluorescent dyes are sometimes used for intraoperative identification of tumors which are depicted as contrast-enhanced lesions by computed tomography (CT) or magnetic resonance images (MRI). Methods using fluorescent dyes for intraoperative tumor identification include: (1)observation of dyes (e.g. fluorescein sodium) which have passed through the damaged blood brain barrier (BBB) [1], and (2) observation of porphyrin derivatives (e.g. porfimer sodium) incorporated into tumor cells. For example, in cases of glioblastoma multiforme, both dyes emit fluorescence in the so-called "active edge" region (Fig. 1), and if surgical resection is confined to this region and to the necrotic area, the patient is unlikely to show postoperative deterioration of neurological symptoms. Thus, fluorescenceguided surgery is very useful in surgical treatment of malignant glioma. Recently, new photosensitizers such as 5-aminolevulinic acid (5-ALA) [2–4], 5-aminofluoresceinalbumin [5] and mono-L-aspartyl chlorine [6] have been developed. This paper will focus on 5-ALA which has been increasingly used clinically.x