Enlarge ImageDramatic but transient. Within 2 months, a novel drug candidate shriveled a man's metastasized cancer (center). One month later, the cancer, now resistant, resurged. Credit: C. M. Rudin et al., NEJM (2009) © Massachusetts Medical Society In the first clinical proof of its kind, a drug has dramatically shrunk cancerous tumors by disrupting a key genetic pathway. But a study targeting one deadly brain cancer, medulloblastoma, ended in disappointment as the patient's once-tamed tumor quickly developed resistance to the drug and killed him. The drug, GDC-0449, was developed at Genentech in South San Francisco, California. It locks onto...