Cancer Stem Cells in Brain Tumors

Some small-sized studies have suggested that CD133 expression and the ability for neurosphere formation have prognostic value in glioblastomas. In a large scale expression study, human glioblastomas were grouped in proliferative, proneural, and mesenchymal tumors. Neural stem cell markers, including CD133 and the formation of neurospheres were upregulated in molecular proliferative subtypes that correlate with a poor prognosis. Thus, CD133 expression and the formation of tumorspheres are completely absent in secondary glioblastomas, which are histologically similar, but different from a molecular point of view with respect to primary glioblastomas. Anaplastic oligodendrogliomas, oligoastrocytomas and glioblastomas with an oligodendroglial component are high grade oligodendroglial tumors, which are difficult to classify because of intratumoral diversity and the absence of clear cut histological markers. It is known that the frequency of tumor sphere growth and a CD133(+) population in high grade oligodendroglial tumors is related with a poor prognosis. Taken together, the presence of CD133(+) stem cells or cell populations with other stem cell biomarkers, and the frequency of tumor sphere formation may become a useful criterion for predicting the response to therapy and for establishing new prognosis glioma subtypes.