When we studied whether stem cell markers are predictors of outcome in subsets of patients with GBM based on MGMT methylation status, we uncovered a remarkable relationship: MGMT methylation was a predictor of outcome only in tumors with strong levels of expression of SOX2 or CD133, and not in tumors with low or absent SOX2 and CD133 expression. The gene discussed is PROM1; the disease is glioblastoma.