Dr. Efstathiou is Professor of Radiation Oncology at Harvard Medical School (HMS), Vice-Chair of Faculty Enrichment in the Department of Radiation Oncology, and Program Director for the Genitourinary (GU) Radiation Oncology Program within the Mass General Brigham Cancer Institute (MGBCI). He earned his undergraduate degree from Yale University, his MD from HMS, DPhil from the University of Oxford, and completed his residency training in the Harvard Radiation Oncology Program.

His busy and robust clinical practice focuses on treatment of patients with prostate, bladder, renal, testicular and other urologic cancers. Delivery of first-rate patient care is a focus. His commitment to clinical excellence, service and mentorship has been recognized as a recipient of numerous awards and honors, as Health Professional of the Game (for the New England Patriots and Boston Red Sox), as a MGH Mentor with Distinction, and as recipient of the A. Clifford Barger Excellence in Mentoring Award from HMS.

He is an internationally recognized leader in GU malignancies and Radiation Oncology. His career has focused on improving outcomes for patients with GU cancers through clinical innovation, clinical trials, translational research, global outreach, advocacy, mentorship, and multidisciplinary care. His research has helped shape clinical guidelines and has advanced organ-preserving approaches in bladder cancer, as well as evaluation of emerging technologies, including proton therapy, in prostate cancer. 

Nationally, he currently also serves as Co-Chair of the National Cancer Institute (NCI) GU Steering Committee, which oversees the national clinical trials portfolio for GU cancers, and as Vice President of the American Society for Radiation Oncology (ASTRO) Foundation. He also serves on patient advocacy organizations including the Bladder Cancer Advocacy Network (BCAN) and on the Board of Directors for the Massachusetts Prostate Cancer Coalition (MPCC).