dr. harold varmus. he's director of the national cancer institute. the institute has helped to lead the work as part of a larger project to map genetic changes in cancer. dr. varmus, thank you for being here. >> my pleasure. woodruff: tell us what is significant about what you found about these four types of breast can iser. >> these four types have actually been known for some time based on work done nearly a decade ago that was intent on characterizing which genes were off and on in breast cancer types. to the surprise of many, it was possible to form four large groups that most breast cancers could fit into. what these studies show -- and they are part of a much larger effort that the cancer institute and the human genome institute are carrying out on many different types of cancer -- is that by using a variety of new techniques to sequence the genome and count the number of copies of genes, to look at which genes are being read out and which proteins are being made that we can look at the heterogeneousity of the cancer of these four groups and fin