In an article published in Science (January 29) scientists in Boston led by Leonard Zon have made a discovery that could change the way one looks at the beginnings and evolution of cancer. Using a model of melanoma in the transparent zebrafish, they addressed the issue as to why do many cells expressing cancer genes never turn cancerous. They found a key switch that causes these cells to revert to an embryonic state initially prior to the beginning of the cancer. This changes radically the view of cancer’s beginnings and opens up new possibilities in treatment.