Dr. Simonds is investigating tumor-initiating cells in pediatric glioblastoma, a type of brain tumor. This rare subpopulation of cells has the unique capacity to re-establish the tumor after therapy, and is therefore a critical therapeutic target. He is using a technique called mass cytometry to determine how these cells respond to communication signals from their environment. The goal of this work is to identify drugs that specifically kill tumor-initiating cells by blocking the signaling networks that sustain their survival.