Timothy J. Ley is the Lewis T. and Rosalind B. Apple Chair in Oncology, Professor of Medicine and of Genetics, director of the Stem Cell Biology Section in the division of Oncology. He specializes in hematology, oncology, leukemia, and cancer biology. An expert on the subject of the physician-scientist career path, Ley has mentored more than 60 pre- and post-doctoral fellows in his laboratory. Ley is a pioneer in the field of cancer genomics, leading the team at the McDonnell Genome Institute that sequenced the first two cancer genomes, from patients with Acute Myeloid Leukemia (AML). This pioneering work has led to an explosion of new studies of the genomes of many cancer types, which has ushered in a new era of understanding of the mutations that cause this disease. Ley and his colleagues have developed genomic methods to understand how AML starts and evolves, and designed methods to track the clearance of AML cells after initial treatment. These approaches are now being used in clinical studies to better define risk of relapse.