Drugs used to treat the tumors common in people with a disorder called neurofibromatosis 1 rarely work, and scientists now know why. The chemotherapy drugs target a group of related proteins, call RAS proteins, which are thought to be responsible for these tumors. But researchers at Washington University School of Medicine in St. Louis found that the disease affects only one member of the protein family, and it happens to be the one form of RAS that does not respond well to these particular treatments.