Dr. Lillian L. Siu is a senior medical oncologist at the Princess Margaret Cancer Centre and Professor of Medicine at the University of Toronto. She serves as Director of the Phase I Trials Program, co-leads the Tumor Immunotherapy Program, and holds the BMO Chair in Precision Genomics. She previously served on the Boards of Directors of the American Society of Clinical Oncology (ASCO) and the American Association for Cancer Research (AACR) and is currently President of AACR (2025–2026).

An internationally recognized leader in early-stage oncology drug development, her work focuses on Phase I clinical trials, biomarker-driven precision medicine, and novel therapeutics for head and neck cancers. She has received numerous honors, including the ASCO David A. Karnofsky Memorial Award and AACR lifetime achievement recognitions, and has authored nearly 400 peer-reviewed publications.

Dr. Siu earned her MD from the University of Toronto and completed her training in internal medicine and medical oncology in Canada and the United States. She currently serves as a member of the MBrace Therapeutics Scientific Advisory Board.