The slimy-smooth, dark-red exterior of a healthy liver yields few clues about its complex nature. This 1.5-kilogram lump of tissue is so good at recovering from injury that it requires as little as one-quarter of its original bulk to fully regenerate. But the organ has its limits. Constant cell damage, such as that caused by a fatty diet, necessitates constant repair, providing the perfect setting for malignancy. Researchers are beginning to unravel how the transition to cancer occurs, with the aim of, eventually, finding more effective ways to prevent it.