In 2003, Sheila Singh and colleagues published “Identification of a Cancer Stem Cell in Human Brain Tumors” in the journal Cancer Research. The study examines a small population of cells within brain cancers that have abilities similar to those of neural stem cells and can maintain the growth of a brain tumor. The researchers identified the brain cancer stem cells by looking at the expression of proteins CD133 and nestin, which are usually present in neural stem cells. In addition, they characterized brain cancer stem cells as having the ability to quickly proliferate and self-renew, form tumor spheres, as well as differentiate in a manner that resembles characteristics of the original brain tumor from which those cells originated. “Identification of a Cancer Stem Cell in Human Brain Tumors” was one of the first studies to identify cancer stem cells in brain cancer and laid the framework for future research investigating the role of brain cancer stem cells in response to treatment, as well as the recurrence of a tumor after treatment.