Growth factor receptors and their ligands.

The understanding of the signal transduction cascade involving growth factors and their receptors is one major key for diagnostic and therapeutic improvements in human neoplasms. Using receptor autoradiography, an inverse relationship for the incidence of somatostatin receptors (SSR) and epidermal growth factor receptors (EGFR) was found in gliomas [1]. In the majority of low grade gliomas, SSR were present but EGFR were absent. In contrast, EGFR were present in most glioblastomas, but no SSR were detected. Recently, the amplification of the EGFR gene and its overexpression was demonstrated to be associated with the development of glioblastomas. Several independent reports revealed that 40-50% of tumors show amplified EGFR [2-4]. The frequency of EGFR amplification was directly associated with tumor malignancy. In addition, amplified EGFR levels indicate a bad prognosis and shorter overall survival [5]. Recent analysis of the EGFR gene in tumors has shown that regions of this gene frequently undergo alteration. Hence, not only amplification but also mutation may be the cause of the increased malignancy in EGFR overexpressing cells [6].