Hematologists are physicians with expertise in the diagnosis and treatment of diseases of the blood and blood-forming tissues. These diseases include disorders of red blood cells, white blood cells, platelets, the immune system, and blood clotting; and hematologic malignancies (such as leukemia, lymphoma, and multiple myeloma). As a result of advances in medical knowledge, many hematologic disorders can be successfully treated.

Hematologists also have special training in transfusion medicine and hematopoietic stem cell transplantation. Many hematologists at Compass Oncology also have training in medical oncology and are board-certified in both disciplines. Like medical oncologists, hematologists work closely with physicians in other specialties, including internal medicine, family practice, surgery, obstetrics and gynecology, and radiation oncology.