One theory of cancer formation holds that some tumors aggressively spread, or metastasize, because they contain a pocket of perpetually renewing cells similar to stem cells. Inspired by this idea, investigators from the Sidney Kimmel Cancer Center in San Diego, Calif., used a mouse model of prostate cancer to identify 11 genes expressed in both neural stem cells and metastatic tumors. They then checked the genes' expression patterns in tissue samples from 1,153 patients treated for one of 11 cancers, including leukemia, lymphoma, and tumors of the breast, prostate and lung. Expression of the signature genes predicted a four-to 20-fold increased likelihood of relapse or death within three to five years, depending on the type of cancer. If confirmed, the signature could help patients and doctors decide whether to adopt aggressive treatment early on, says Gennadi Glinsky, co-author of the June 1 Journal of Clinical Investigation report.