What Is a Hematologist Oncologist?

A hematologist-oncologist is a physician who specializes in the diagnosis, treatment and prevention of blood diseases and cancers including iron-deficiency anemia, hemophilia, sickle-cell disease, leukemia and lymphoma. This physician is trained in hematology (the study of blood) and oncology (the study of cancer). Most hematologist-oncologists focus on oncology, particularly solid tumors, and acquired hematologic conditions that affect the blood.

Hematologist-oncologists do not usually treat operable cancers such as prostate cancer, but specialize in treating blood cancers, such as Hodgkin’s disease and non-Hodgkin’s lymphomas, leukemias and multiple myelomas. A hematologist-oncologist may also specialize in the management of solid tumors, or other types of specialized tumors.

Pediatric Hematologist-Oncologist

Most hematologic disorders and malignancies occurring during infancy, childhood, and adolescence are uncommon and require a highly sophisticated approach to diagnosis and treatment based on molecular and cellular biology, epidemiology, and other academic disciplines (Buchanan, 2017).  Pediatric hematology-oncologists mainly focus on genetic hematologic disorders such as sickle-cell disease, hemophilia, or von Willebrand disease, leukemia, and embryonal tumors.

Pediatric hematologist-oncologists work closely with other medical specialists including radiologists and pathologists, laboratory hematologists and cytogeneticists. These other specialists have little to no direct patient contact, as the hematologist-oncologist does. Pediatric surgeons, radiation oncologists, and infectious disease specialists may also coordinate patient care with a pediatric hematologist-oncologist.

Today pediatric hematology-oncology specialists are involved with a wide range of tumors, from hemangiomas and other benign vascular malformations to malignant brain neoplasms (Buchanan, 2017).  There are approximately 1,900 pediatric hematology-oncology specialists who have been certified by the American Board of Pediatrics (ABP) since the first examination in 1974. Currently, nearly 1,365 pediatric hematology-oncology specialists are licensed to practice in the United States. For reference, there are around 53,000 general pediatricians currently practicing in the U.S.

The need for physicians trained to diagnose and treat children with cancer and hematologic disorders remains strong, as the incidence of most of the diseases treated by hematologist-oncologists is not decreasing, and some are becoming more common (Buchanan, 2017). Cancer is the leading disease, causing death in children younger than 15 years of age, although survival rates for most childhood cancers have increased. Cure rates for all childhood cancers are approximately 75%, and most centers have “off therapy” programs to follow these children (Buchanan, 2017).

Pediatric Hematology-Oncology Career Options

Though widely varied, the most common pathway after completing a fellowship is a position as an instructor or assistant professor of pediatrics in an academic pediatric hematology-oncology division. (Buchanan, 2017).  The daily activities of a pediatric hematologist-oncologist vary and are unpredictable, although some primary duties may include diagnosing and caring for children with blood diseases and cancer, teaching medical students, residents, fellows, and other healthcare professionals, and conducting clinical research through case studies and clinical trials (Buchanan, 2017). Most educational activities are with individuals, as opposed to large seminars or lectures.

Some pediatric hematology-oncology specialists continue with additional training post-fellowship to focus on laboratory research or experiences in basic science laboratories, or in translational research areas of pediatric hematology-oncology. These specialists have some clinical duties, but they spend most of their time conducting research to determine the cause of childhood diseases and discover improved treatments, in addition to identifying the biological aspects of diseases such as cancer.

Clinical investigation is another career option for pediatric hematology-oncology specialists. Clinical investigation involves extensive training in epidemiology, biostatistics, protocol design, and public health. These specialists conduct studies to determine the nature of a particular disease, and develop treatment strategies via randomized clinical trials or health services research. Some specialists who wish to focus on clinical investigation obtain a Master’s Degree in Public Health.

Other career opportunities in pediatric hematology-oncology may include administrative positions, such as a division chief, department chair, or dean, while other options may include private practice or opportunities in pharmaceutical specialties. Some pediatric hematology-oncology specialists emphasize clinical oncology, or expertise in solid tumors (or other specific types of tumors like neuroblastoma or bone tumors in their career. Others may focus on acute leukemia, neuro-oncology, cancer pharmacology, or the development of experimental agents (Buchanan, 2017).

Bone marrow, or stem cell, transplantation is an emerging field, and some pediatric hematology-oncology specialists devote most or all of their time diagnosing and caring for the transplant patient and conducting clinical, translational, or laboratory research in transplantation (Buchanan, 2017).  Some individuals deal primarily with nonmalignant hematology and become experts in sickle-cell disease, hemophilia, thrombotic disorders, or quantitative or qualitative disorders of neutrophils (Buchanan, 2017).

Bone Marrow, Blood, and Lymphoid Tissue

Bone Marrow

Bone marrow is the soft inner section of certain bones, including the skull, shoulder blades, ribs, and pelvis. It is comprised of blood stem cells, more mature blood-forming cells, fat cells, and other tissues that support cell growth. The blood forming cells mature into either red blood cells, white blood cells, or platelets. White blood cells may be lymphocytes, granulocytes, or monocytes.

Red Blood Cells

Red blood cells transport oxygen from the lungs to all tissues throughout the body, and return carbon dioxide back to the lungs for removal. Platelets are cell fragments made by the megakaryocyte in the bone marrow. Platelets have a significant role in blood clotting.

White Blood Cells

White blood cells work as part of the immune system to resist infections. Lymphocytes are the building blocks of lymphoid tissue, which is a significant part of the immune system, and it is found in lymph nodes, the thymus, spleen, and tonsils and adenoids. It is also found in the digestive and respiratory systems, and in bone marrow.

Lymphocytes develop from cells called lymphoblasts to become mature, infection-fighting cells (ACS, 2017). B-lymphocytes mature into plasma cells, which protect against bacterial infections. B-lymphocytes make antibodies, which locate and destroy bacteria, viruses, and fungi. T-lymphocytes are also known as T-cells, and they have a variety of functions within the immune system.

Granulocytes are white blood cells that have enzymes (or granules) that are identified by the size and color of the granules when viewed under a microscope. Neutrophils, basophils, and eosinophils are the three types of granulocytes. Neutrophils are pink, basophils are dark blue, and eosinophils look bright red.


Neutrophils (UWOSH, 2017): The neutrophils make up the majority (50-75%) of the total white blood cells in a normal person's blood. A mature neutrophil has a segmented nucleus and is twice the size of a red blood cell. A segmented nucleus means that you can see two to five segments (aka- lobes) of nucleus in one cell. The granules in a neutrophil are small, numerous, and are stained a light-pink to bluish-purple, "neutral" color. The cytoplasm of a neutrophil is light pink.

When a person is fighting infection, the granules may be dark colored, which is called toxic granulation. One type of anemia causes the neutrophils to be hyperlobulated, which means that many of the neutrophils have six or more lobes to their nucleus. Whenever a person experiences any kind of inflammation, the neutrophils are the first to the scene.


Basophils account for the least amount of the granulocytes. They are present as one percent or less of a person's white blood cells, and their large granules are a deep blue-purple color. Their nucleus is also segmented.


Eosinophils grab onto lots of eosin dye when they're stained, making their large granules a red color. The granules in an eosinophil usually cover the nucleus, but sometimes you can see that the nucleus is segmented. Eosinophils are not as common in the blood as neutrophils. They're usually less than three percent of a person's total white blood cells, but people with allergies may have a larger percentage of eosinophils. Their primary job is to be involved in allergic reactions, eosinophils are also increased when a person has a parasite. For example, a person with a tapeworm in their digestive tract will have an elevated eosinophil count (UWOSH, 2017).


Monocytes are white blood cells that circulate throughout the bloodstream before entering tissues to become macrophages. Monocytes are large – they are around three to four times the size of a red blood cell.  However, thy only account for one to six percent of the blood stream. Monocytes can be difficult to differentiate from lymphocytes, but they usually have a larger amount of cytoplasm in relation to the size of the nucleus. They are also usually more irregular in shape than the smooth lymphocytes. You can sometimes see "pseudopods" on monocytes, the "fake feet" that help it move and digest foreign particles (UWOSH, 2017).

The cytoplasm of a monocyte is a dull blue-gray color. Even though they are not granulocytes, monocytes have granules.  They are very fine and lightly stained, giving the monocyte cytoplasm a "ground-glass" appearance. You may also see vacuoles, which look like holes in the cytoplasm. When a monocyte has vacuoles, you know it has been hard at work (UWOSH, 2017). The vacuoles contain chemicals that digest the foreign particles such as bacteria.

Lymphocytes (ACS, 2017):

The lymphocytes and monocytes belong to the mononuclear cell group, which means their nucleus is in one piece, and not segmented. There are almost as many lymphocytes as neutrophils in the blood. Lymphocytes are special because they can become "memory cells". When doctors talk about a person being "immune", they are referring to the ability of that person's lymphocytes to remember a foreign invader.

When a person is exposed to a new infectious agent, some of their lymphocytes make antibodies against it. The rest of the lymphocytes remember that infectious agent and get the immune system working faster the next time a person is exposed to that infectious agent. Very young children have more lymphocytes than adults because they are developing immunity to the many new infectious agents around them. Lymphocytes make up 20-40 percent of an adult's total white blood cells.

Small lymphocytes have a round nucleus and a small amount of blue cytoplasm. Overall, the lymphocyte looks very smooth and round. Lymphocytes vary a lot. They can be larger with a lot of cytoplasm when they are encountering an infectious agent.


Leukemia is a cancer of blood-forming cells in their earliest stages. Although it is most common in white blood cells, this blood cancer may start in other blood cell types as well. Leukemia may be acute or chronic, and it is categorized into different types due to the blood cells and other aspects of the disease. Acute leukemia progress quickly, and can be fatal if untreated. Chronic leukemia slowly progresses over time, although it can eventually be fatal as well.

Acute Leukemia (ACS, 2017): In acute leukemia, the bone marrow cells cannot mature properly. Immature leukemia cells continue to reproduce and build up. Without treatment, most people with acute leukemia would live only a few months. Some types of acute leukemia respond well to treatment, and many patients can be cured. Other types of acute leukemia have a less favorable outlook.

Chronic Leukemia (ACS, 2017): In chronic leukemia, the cells can mature partly but not completely. These cells may look fairly normal, but they generally do not fight infection as well as normal white blood cells do. They also live longer, build up, and crowd out normal cells. Chronic leukemias tend to progress over a longer period of time, and most people can live for many years. But chronic leukemias are generally harder to cure than acute leukemias.

Acute Lymphocytic Leukemia (ALL)

Acute Lymphocytic Leukemia (ALL) begins in the bone marrow, where blood cells are produced, and it is more common in children than in adults. Leukemia cells invade the blood quickly, and then they spread to other parts of the body, including the lymph nodes, liver, spleen, central nervous system, and testicles (in males).

Lymphomas, such as non-Hodgkin lymphoma or other Hodgkin disease, are cancers that being in the lymphocytes. Some cancerous lymphocytes are found in both the bone marrow and lymph nodes, so it can be difficult to decipher the root cause and type of the cancer. If more than 25% of the bone marrow is replaced by cancerous lymphocytes, the disease is usually considered leukemia, although the size of lymph nodes is also important - the bigger they are, the more likely the disease will be considered a lymphoma (ACS, 2017).

According to the ACS (2017), nearly 5,970 new cases of ALL were estimated for 2017, and around 1,440 deaths occurred due to ALL. Slightly more males than females are affected by ALL.

Other Types of Leukemia

Acute Myeloid Leukemia (AML) is also referred to as acute myelocytic leukemia, acute myelogenous leukemia, acute granulocytic leukemia, or acute non-lymphocytic leukemia, and it is most common in adults.

Chronic Lymphocytic Leukemia (CLL) begins in the white blood cells, which are also known as lymphocytes, in the bone marrow. Nearly one-third of all leukemias are the CLL type, although this is most common in adults.

Chronic Myeloid Leukemia (CML) is also known as chronic myelogenous leukemia. CML begins in blood-forming cells of the bone marrow and enters the bloodstream. Approximately 10% of leukemias are CML.

Chronic Myelomonocytic Leukemia (CMML) is a cancer that begins in the blood-forming cells of the bone marrow that affects mostly adults.


Lymphoma is a cancer that beings in the cells of the body’s immune system. There are several different types of lymphomas, although Hodgkin’s lymphoma is one of the most common.

Hodgkin Lymphoma can begin in any of the multiple lymph nodes throughout the body. The major sites of lymph nodes are (ACS, 2017):

Lymph nodes: Lymph nodes are bean-sized collections of lymphocytes and other immune system cells throughout the body, including inside the chest, abdomen, and pelvis. They are connected to each other by a system of lymphatic vessels.

Spleen: The spleen is an organ under the lower ribs on your left side. The spleen makes lymphocytes and other immune system cells. It also stores healthy blood cells and filters out damaged blood cells, bacteria, and cell waste.

Bone marrow: The bone marrow is the spongy tissue inside certain bones. New blood cells (including some lymphocytes) are made there.

Thymus: The thymus is a small organ behind the upper part of the breastbone and in front of the heart. It is important for T lymphocyte development.

Adenoids and tonsils: These are collections of lymphoid tissue in the back of your throat. They help make antibodies against germs that are breathed in or swallowed.

Digestive tract: The stomach, intestines, and many other organs also have lymph tissue.

Although Hodgkin lymphoma can start almost anywhere, most often it starts in lymph nodes in the upper part of the body. The most common sites are in the chest, neck, or under the arms. 

Hodgkin lymphoma most often spreads through the lymph vessels from lymph node to lymph node. Rarely, late in the disease, it can invade the bloodstream and spread to other parts of the body, such as the liver, lungs, and/or bone marrow.

A Brief History of Hematology-Oncology

The link between pediatric hematology and oncology has a historical basis (AAP, 2017).  Acute leukemia is considered the most serious of common cancers, and it typically occurs in children. Since leukemia is also a cancer of the blood, it was often treated by a hematologist, as opposed to an oncologist. As chemotherapy and other treatment approaches were developed during the 1950s and 1960s, these hematology specialists, who were familiar with cancer chemotherapy, began to also care for and study children with solid tumors (AAP, 2017).

How to Become a Hematologist-Oncologist

To become a hematologist-oncologist, you will need over a decade of education and training. An undergraduate degree, completion of medical school and a residency program are all required to become a licensed oncologist. Many hematologist-oncologists who pursue a subspecialty obtain an additional certification, although this is optional.  Licensing, however, is mandatory.

As mentioned above, the first step to becoming an hematologist-oncologist is to obtain a bachelor’s degree.  Many future hematologist-oncologists major in biological science, chemistry, physics or pre-medical, although there is no specific requirement for a major. Science programs typically have the classes and subjects that meet the standards to admittance into medical school.

Medical School

The Medical College Admission Test (MCAT) will be taken during the third year of undergraduate study. Medical schools use this exam as a skills assessment to evaluate an applicant’s training and knowledge. In addition to the minimum requirements, volunteering at a hospital or medical center not only allows for hands-on training working with patients, but it may help an applicant stand out to the medical evaluation board.  Participation in extracurricular activities and learning a foreign language may also be beneficial in standing out and increasing the chances of acceptance into medical school.

Medical school typically consists of a four-year program.  The first two years focus on classroom instruction of anatomy and physiology, biochemistry, pathology and pharmacology.  The last two years includes hands-on clinical training covering specialized medicinal areas such as pediatrics or surgery.  A Doctorate of Medicine (M.D. or Phd.) is rewarded after successful completion of the 4-year medical school program.


After graduation from medical school, a 3 to 4-year residency must be completed. Many oncologists obtain internal medicine residency training, although a pediatric hematology-oncology specialist will complete a residency in pediatrics.

Surgical hematologist-oncologists must first complete a general surgery residency 5-year program before pursuing a 3-year surgical oncology fellowship for specialized tumor surgery training. Pediatric and gynecological oncologists also complete additional fellowship training in their sub-specialty field.


Hematologist-oncologists pursuing a subspecialty will need a fellowship program in order to gain the additional skills and training required. A fellowship typically lasts two years. When the residency or fellowship is completed, the aspiring oncologist will take the licensing exam and if they choose, apply for board certification. Certification is offered by the American Board of Internal Medicine (ABIM), American Board of Pediatrics (ABP), American Board of Radiology (ABR) or the American Board of Surgery (ABS).

Although many hematologist-oncologists practice in hospitals, others may be employed at medical centers, pediatric hospitals, surgical centers, outpatient clinics, nursing homes, prisons, public health centers, health care organization and within many other industries (Doctorly, 2017). Some may also choose to open their own private practice. Other career opportunities include college or university settings in an academic position, and clinical research, where the oncologist is devoted solely to researching treatment alternatives or performing studies for pharmaceutical development.





Buchanan, George R., M.D. Career in Pediatric Hematology-Oncology? American Society of Pediatric Hematology/Oncology. Retrieved December 15, 2017 from:  https://www.aap.org/en-us/about-the-aap/Committees-Councils-Sections/section-hematology-oncology/Documents/career_brochure.pdf


ACS – American Cancer Society. Leukemia. 2017. Retrieved December 4, 2017 from: https://www.cancer.org/cancer/leukemia.html


UWOSH – University of Wisconsin Oshkosh. 5 Common Types of White Blood Cells. 2017. Retrieved December 5, 2017 from: http://www.uwosh.edu/med_tech/what-is-elementary-hematology/white-blood-cells


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