His scientific career has focused on the biology and treatment of breast cancer. He has been a major leader in the science of cancer stem cells. His group was part of the team that first identified breast cancer stem cells, the first such cells identified in solid tumors. His laboratory has identified a number of cancer stem cell markers and developed in vitro and mouse models to isolate and characterize these cells, models which have been widely utilized in the field. His group has subsequently elucidated a number of intrinsic and extrinsic pathways which regulate stem cell self-renewal and cell fate decisions. This work has directly led to development of several clinical trials aimed at targeting breast cancer stem cells. Under his leadership, the University of Michigan Rogel Cancer Center established itself as one of the nation’s premier cancer centers. He was also recently appointed by President Obama to the National Cancer Advisory Board (NCAB). This board advises the NCI Director and Secretary of Health on matters related to cancer research and health policy.