Growth factors in gliomas revisited

Overexpression or untimely expression of wild-type or mutated protein growth factors and their receptors is associated with the biology of malignant gliomas and other types of cancer. It may result in unchecked tumour cell proliferation, migration/invasion into normal tissue, tumour angiogenesis, escape from immune surveillance, and decreased apoptotic cell death, i.e. after treatment with cytotoxic agents. This often involves activation of growth factor receptors either by simultaneous production of growth factors and corresponding receptors on the same or adjacent tumour cells or by constitutive receptor activation due to mutations. In several instances, the cellular genes encoding these growth factors and receptors are homologous to transforming genes/oncogenes from tumourigenic retroviruses and have thus been regarded as cellular proto-oncogenes. In recent years much progress has been made towards a better understanding of the function of these molecules and how they lead to the aggressive phenotype of malignant gliomas and its inherent resistance to adjuvant therapies. This, still insufficient, knowledge is a prerequisite for the development of novel therapies for this non-curable disease. The aim of this review is to address relevant growth factor receptor systems with emphasis on their particular role in glioma biology.