The Epigenetic landscape model compares cells to marbles rolling down rivulets of a valley. Some scientists believe cancer cells jump between rivulets, overwhelming normal cells. Jesse Dill/http://www.flickr.com/photos/jwdill/2514534670/in/photostream/ hide caption

itoggle caption Jesse Dill/http://www.flickr.com/photos/jwdill/2514534670/in/photostream/