Not just another biomarker: the role of integrin alpha 7 in glioblastoma

Glioblastoma is the most lethal primary brain tumor, and one of the most aggressive and invasive types of cancer overall. Despite treatment efforts, median length of survival for glioblastoma patients is between 12 and 18 months (1). Aside from their aggressive nature, glioblastomas are also known for being heterogeneous, with many different cell types throughout the tumor. Glioblastoma stem cells (GSCs) are one cellular subtype within these tumors and are characterized by unlimited self-renewal and resistance to treatment. Cancer stem cells have been identified in brain tumors as well as other cancers, and are thought to play a central role in the malignancy of these tumors (2,3). Hence, there is huge interest amongst researchers to find ways to target the cancer stem cell population specifically. Knowing which cells within a tumor are the extremely tumorigenic GSCs is not possible without reliable biomarkers. As mentioned previously, glioblastomas are heterogeneous within each individual tumor, but are also heterogeneous from one patient to the next. Many groups have identified markers of cancer stem cells that turn out to have greater representation in certain subtypes over others, such as CD44 in mesenchymal tumor regions, and CD133/Olig2 in proneural tumor regions (4-7). Despite the wide use of these surface epitopes as biomarkers, there is still controversy over whether or not they are uniformly reliable across patient samples (2).