Medical specialties will often feature a degree of overlap, because events in one part of the body often affect other areas. Some specialties have especially close relationships, such as obstetrics and gynecology or hematology and oncology. Although hematology and oncology are separate areas of medical practice, they intersect often enough that many physicians train in both areas.
Hematology represents the branch of medicine concerned with illness and conditions of the blood and systems such as bone marrow and lymph nodes that are directly related to blood. These include hemophilia and other clotting disorders, anemia and various malfunctions of the bone marrow and white blood cells. Hematologists also treat cancers of the blood and lymph nodes including Hodgkin's disease, non-Hodgkin's lymphoma and various forms of leukemia.
Oncology is the branch of medicine that diagnoses and treats cancers. Surgical oncologists and radiation oncologists remove cancers physically or attack them with radiation, while medical oncologists administer chemotherapy and other forms of medication. Medical oncologists are usually responsible for diagnosing the cancer and determining its type and extent, and they'll coordinate a patient's care in collaboration with surgeons and other practitioners. Chemotherapy, surgery and radiation are all effective in treating some cancers, and deciding which techniques are appropriate for each patient is a major part of the oncologist's role.
Both oncology and hematology are branches of internal medicine. After qualifying as internists through a three-year residency, doctors can specialize by spending two years in a hematology or oncology fellowship. Alternatively, they can opt for a single three-year fellowship that combines both specialties. Individual oncologists, hematologists or hematologist-oncologists can decide how narrowly or broadly they'll practice. For example, some might specialize in leukemia and anemia, avoiding cancers entirely. Others might focus on Hodgkin's disease and non-Hodgkin's lymphoma, while seldom treating blood diseases or other cancers.
For physicians entering the field, both hematology and oncology offer promising career paths. The U.S. Bureau of Labor Statistics has projected 24 percent employment growth for physicians and surgeons between 2010 and 2020, well above the national average of 14 percent for all occupations. The bureau notes that prospects are best for physicians treating the elderly, as the population -- and especially the large baby boom generation -- grows older. Many cancers become more common with age, so more hematologist/oncologist specialists are needed.