Dr. Mattar received his medical degree from St. Joseph University School of Medicine, Beirut, Lebanon in 1993. He completed his internal medicine residency at the University of Kansas School of Medicine – Wichita, Kansas. Dr. Mattar also completed a fellowship in Oncology/Hematology and Bone Marrow Transplantation at the University of Alabama, Birmingham, Alabama, in 1999. Following the completion of his fellowship in 1999, he joined the Cancer Center of Kansas team. He is board certified in Internal Medicine, Medical Oncology and Hematology. He is a member of the American College of Physicians, the American Society of Clinical Oncology, the American Society of Hematology, the Southwest Oncology Group and the American Society for Blood and Marrow Transplantation. Dr. Mattar continues to be active in clinical cancer research as a Principal Investigator in our Wichita NCI Community Oncology Research Program, a National Cancer Institute sponsored program, and other areas of clinical research with interest and expertise in allogeneic bone marrow transplantation.

He was promoted to Clinical Professor of Internal Medicine at the University of Kansas School of Medicine in 2023, formerly a Clinical Assistant Professor from 1999 to 2023.  In 2005, Dr. Mattar became the Director of the Blood and Marrow Transplant Program, which is an integrated program of the Cancer Center of Kansas, America Red Cross and Ascension Via Christi Hospital St. Francis and in 2021 was renamed to Cellular Therapy Center of Kansas. Since joining the Cancer Center of Kansas in 1999, he has greatly contributed to the mission of the center, providing the highest quality patient care with the latest advances in clinical cancer research.