Only 1-2% of the entire population within a glioblastoma are glioma stem cells (also called tumor initiating cells). This cell population is characterized by specific gene expression profiles and an inherent resistance against cytotoxic stress. Under radiation and chemotherapy glioma stem cells survive and repopulate the tumor leading to recurrence of bulk tumor. The molecular characteristics and resistance mechanisms active in individual glioma stem cell lineages will determine the response to any treatment strategy for recurrent glioblastoma.
Stemness is characterized by clonogenic and tumorigenic growth in an undifferentiated state. Asymmetrical division results in tumor cell strains of varying differentiation and phenotypes resulting in a more or less heterogeneous recurrent tumor.