MICHAEL F. CLARKE and MICHAEL W. BECKER worked together in Clarke's laboratory at the University of Michigan at Ann Arbor, where breast tumor stem cells were first isolated in 2003. Clarke is now associate director, as well as professor of cancer biology and of medicine, at the Stanford Institute for Stem Cell Biology and Regenerative Medicine. He continues to work on identifying cancer stem cells and the mechanisms by which they, as well as normal stem cells, regenerate. Becker is assistant professor of medicine in the hematology and oncology division of the University of Rochester Medical Center. Becker's research focus is characterizing leukemic stem cells, and his clinical work centers on peripheral blood and bone marrow transplantation.