Dr. Lessnick earned his bachelor's degree from Brandeis University, followed by MD and PhD degrees from the University of California, Los Angeles (UCLA), as part of the Medical Scientist Training Program (MSTP). He did his PhD thesis with Christopher Denny, MD, where he studied the function of the Ewing sarcoma EWS/FLI oncoprotein. He then conducted his internship and residency at Children's Hospital in Boston, Massachusetts, followed by a fellowship in pediatric hematology/oncology at Children’s Hospital and Dana-Farber Cancer Institute in Boston. He completed postdoctoral research in the Pediatric Oncology Department at the Dana-Farber Cancer Institute with Todd Golub, MD, where he studied the transcriptional consequences of EWS/FLI.
Dr. Lessnick joined University of Utah faculty in January 2004 and rose through the ranks to become a Tenured Professor of Pediatrics in the Division of Pediatric Hematology/Oncology, a Jon and Karen Huntsman Presidential Professor in Cancer Research, and the Director of the Center for Children's Cancer Research at Huntsman Cancer Institute. In July 2015, Dr. Lessnick joined the faculty at The Research Institute at Nationwide Children’s Hospital as the director of the Center for Childhood Cancer and Blood Diseases and The Ohio State University as a professor of Pediatrics in the Division of Pediatric Hematology/Oncology.