Two vaccines effective against non-small- cell lung cancer, the most common type of cancer to affect that organ, are the most likely. In a 2004 study, patients who got Stimuvax, manufactured by Merck KGaA, lived on average 17.3 months longer than unvaccinated patients. A similar vaccine by GlaxoSmithKline is also in clinical trials. "Within five years, I think we'll see several more vaccines approved," says James Gulley, a medical oncologist at the National Cancer Institute who is studying a new type of prostate-cancer vaccine called Prostvac. Scientists are currently testing vaccines against ovarian, liver and pancreatic cancers. Several cancer vaccines have already been approved outside the U.S., including ones against skin and colon cancers.