Hematology is the medicine of blood and the problems that affect it, while oncology is the medicine of cancer wherever it grows in the body.1American Cancer Society. What Is Hematology? Much of a hematologist’s work has nothing to do with cancer, so being sent to one is not the same as being told you might have it. The two fields meet in cancers of the blood, which is why so many clinics and doctors carry both names on the door.
What a Hematologist Treats
Hematology covers how blood is made and how each part of it works. The field looks at red cells that carry oxygen, white cells that fight infection, platelets, bone marrow, lymph nodes and the proteins that make blood clot.2UPMC. About UPMC Hematology Services A problem with any of these, from too few red cells to blood that clots too easily, falls to a hematologist.
Most of the field is non-cancer conditions. Hematology splits into non-cancer blood conditions, often called benign hematology, and blood cancers.3American Cancer Society. What Is Hematology? On a referral letter, “benign” means not cancer. It does not necessarily mean mild, and some conditions, like severe clotting disorders, still need close care.
The non-cancer side includes anemia, heavy or unexplained bleeding, and blood clotting problems.4American Cancer Society. What Is Hematology? In one large cancer center, anemia made up about a quarter of accepted non-cancer blood referrals and clotting disorders about a fifth.5PubMed. Classical Hematology Referrals at an National Cancer Institute-Designated Cancer Center: Lessons Learned Everyday reasons people meet a hematologist include iron deficiency that doesn’t improve with pills, a blood clot in the leg or lung, easy bruising or heavy periods, and low or high counts found on a routine blood test.
Hematologists often work as consultants. Your primary doctor or another specialist sends a question, such as why your hemoglobin is low, and the hematologist works out the cause and recommends a plan. Many low red cell counts come from something outside the blood itself, such as slow blood loss, a vitamin shortage, kidney disease or long-term inflammation, so the first job is finding the cause rather than assuming a marrow problem. Some people stay with a hematologist for years because inherited bleeding disorders or sickle cell disease need ongoing management, while others are seen once or twice and sent back to their regular doctor.
Other specialists often work on the same problem. A gastroenterologist may look for the bleeding source behind iron deficiency, and a gynecologist may treat the cause of heavy periods. The hematologist’s focus is the blood side: whether the clotting system, the iron stores or the cell production is the issue.
Inherited blood disorders are a big part of the work. Inherited hemoglobin disorders include thalassemia and sickle cell disease, and they range from mild anemia to severe lifelong anemia that needs regular transfusions.6PubMed Central. Hemoglobinopathies Hemophilia, an inherited bleeding disorder, needs careful handling of any blood-thinning medicine.7PubMed Central. Antithrombotic Treatment in Patients With Hemophilia: an EHA-ISTH-EAHAD-ESO Clinical Practice Guidance
What an Oncologist Treats
The oncologist most people mean is a medical oncologist, who practices what we’ll call cancer medicine: treating cancer with drugs such as chemotherapy, immunotherapy and targeted therapy.8EBSCO. Medical oncology These medicines travel through the whole body and can reach cancer cells beyond the original tumor, unlike surgery on one spot.9OncoDaily. Surgical Oncology vs Medical Oncology: Who Does What in Cancer Care They’re often used when cancer may have spread or to lower the chance it returns.
This kind of treatment is usually given as a pill or through a vein. The tradeoff is that healthy cells elsewhere can also be affected, which is why side effects such as fatigue, nausea or low blood counts are discussed up front.
The drug types are not the same thing. Chemotherapy generally targets cells that divide quickly, which is why it also affects hair, the gut lining and bone marrow. Targeted therapy is aimed at a specific feature found in a particular cancer, which is why tumor testing comes first. Immunotherapy helps the immune system recognize cancer rather than attacking the cancer directly. Some people receive more than one type, and the mix depends on the cancer.
Treatment choices are tailored. The oncologist weighs the cancer type, its stage, features of the tumor, earlier treatments and your overall health.10OncoDaily. Surgical Oncology vs Medical Oncology: Who Does What in Cancer Care Genetic testing of tumor tissue can check hundreds of cancer-related genes at once,11PubMed Central. Development and validation of a clinical cancer genomic profiling test based on massively parallel DNA sequencing so two people with the same cancer name may get different drugs.
Most oncology patients have solid tumors, which are cancers that form a lump in an organ such as the breast, lung or colon. These are staged by size and spread. Blood cancers often don’t form a single lump, so they’re tracked differently, as the next section explains.
Oncology is a team with several kinds of oncologist. Surgical oncologists remove tumors and radiation oncologists use radiation, while medical oncologists work alongside them.12Fox Chase Cancer Center. Multidisciplinary Cancer Care: What It Means and Why It Matters Many centers review each case at a joint meeting with all three plus imaging and lab specialists.13Oncology Practice Management. Multidisciplinary Care, a Paradigm Shift
In practice, your medical oncologist is often the main ongoing doctor during drug treatment, while surgeons and radiation doctors are seen for set periods. It’s reasonable to ask who coordinates your care.
Where the Two Fields Overlap
Blood cancers include leukemia, lymphoma and multiple myeloma.14American Cancer Society. What Is Hematology? They often start in the bone marrow, where blood cells are made,15Association of Cancer Care Centers. Hematologic Malignancies so treating them needs knowledge of both normal blood and cancer drugs. A cancer growing there can crowd out healthy production and cause anemia, infections or bruising. That is why blood cancers can first show up as abnormal blood counts rather than as a lump. Telling a marrow cancer apart from a non-cancer cause of the same low counts takes the blood expertise hematologists have.
Training reflects the overlap. In the US, board certification in hematology or medical oncology alone takes two years of fellowship training.16Vagelos College of Physicians and Surgeons. Board Certification Requirements Training in both takes three years, often split evenly between them.17Lenox Hill Hospital. Fellowship in Hematology & Medical Oncology at Lenox Hill Hospital A doctor listed as “hematology/oncology” is certified to handle both blood disorders and cancers.
That label describes the doctor’s training, not your diagnosis. The same office sees anemia patients and chemotherapy patients, so if you’re unsure why you were sent, ask the referring doctor. A doctor with both certifications can evaluate a puzzling blood test and, if cancer turns out to be the answer, continue treating you without a handoff. If the answer is a non-cancer condition, the same doctor manages it.
Some centers split them instead. Some hospitals send non-cancer blood conditions to hematologists and blood cancers to their cancer center team.18UPMC. About UPMC Hematology Services
Why You Might Be Referred
Common reasons for referral include:
- Low red cells, white cells or platelets on a blood test19Hematology Oncology Associates Of Fredericksburg. First Visit to a Hematology Oncologist: What to Expect
- Blood clotting or bleeding problems20Hematology Oncology Associates Of Fredericksburg. First Visit to a Hematology Oncologist: What to Expect
- Anemia or iron disorders21Hematology Oncology Associates Of Fredericksburg. First Visit to a Hematology Oncologist: What to Expect
- A known or suspected cancer, including leukemia, lymphoma or myeloma22Hematology Oncology Associates Of Fredericksburg. First Visit to a Hematology Oncologist: What to Expect
A referral usually means a result or symptom needs a closer look than a general doctor can give. Abnormal counts can come from infections, medicines, nutrient shortages or inherited traits, and these are all more common than blood cancer.
Many referrals end with a non-cancer explanation like iron deficiency. It’s fine to ask for a call with results.
Useful questions for the referring doctor: which result prompted the referral, whether it’s urgent or routine, what tests to expect first, and whether to keep taking any medicines like iron or blood thinners until the visit.
Persistent fever, unexplained weight loss, drenching night sweats, swollen glands that do not settle or unusual bleeding are worth reporting if they continue while you wait. If symptoms get worse before the appointment, call the referring office rather than waiting for the date.
How Each Specialty Makes a Diagnosis
Hematology starts with blood. A complete blood count, listed as “CBC” on your report, measures your red cells, white cells and platelets. The report lists each measurement beside a reference range, and values outside it are usually flagged. A flag does not automatically signal disease, since normal ranges are set statistically and a slight deviation can be harmless. A hematologist looks at the pattern, such as whether one cell type is off or several, and compares with earlier results. A trend over time often tells more than a single number.
If the machine flags something, a specialist looks at your blood under a microscope on a slide called a smear.23PubMed Central. Purpose and Criteria for Blood Smear Scan, Blood Smear Examination, and Blood Smear Review A machine counts cells but cannot fully judge their shape, so the specialist checks size, shape and maturity. Unusual shapes can point to causes such as iron deficiency, vitamin shortage or inherited conditions, and immature cells in the blood can prompt further tests such as a bone marrow sample. Blood and bone marrow samples are the basis for diagnosing both non-cancer and cancer blood disorders.24PubMed. Digital assessment of peripheral blood and bone marrow aspirate smears
A marrow test takes a sample from the back of the hip bone with a needle. It’s done with local numbing, often in clinic, and usually takes under half an hour. Soreness lasts a few days.
Oncology starts with the tumor. Solid tumors are diagnosed with imaging and a tissue biopsy, then staged by size and spread.25Advanced Practice Providers Oncology Summit – APPOS. Understanding Solid Tumor Staging: Implications for Patient Care (Through Jan 24, 2026) – Advanced Practice Providers Oncology Summit – APPOS
Results arrive at different speeds. Blood counts come back fast, smear and marrow reviews take longer, and genetic tests can take weeks.
How Treatments Differ
Non-cancer blood care uses a fairly familiar toolkit: iron pills or infusions for iron deficiency, blood thinners for clots, transfusions for some inherited anemias, and clotting factor replacement for hemophilia.
Solid tumor care often combines surgery, medicine and radiation, with the order depending on stage. The medical oncologist manages the drug part.
Blood cancer outlooks have improved. Over 70% of people with Hodgkin lymphoma can be cured, and about half or more of people with other lymphomas can be cured.26PubMed. The hematologic malignancies. Leukemia, lymphoma, and myeloma A cure means the cancer is gone and not expected to return, whereas control means treatment keeps it in check, sometimes for years. Some blood cancers, such as certain forms of myeloma, are often managed as long-term conditions rather than cured. Your oncologist can tell you which goal applies to your diagnosis.
Some treatments are unique to blood cancers. A stem cell transplant can cure some blood diseases.27PubMed Central. Transfusion support in hematopoietic stem cell transplantation Some use your own stem cells, mostly for myeloma and lymphoma, while others use a donor, mostly for leukemia.28PubMed Central. Transfusion support in hematopoietic stem cell transplantation Before a transplant, high-dose treatment clears diseased marrow, and then healthy stem cells are infused through a vein. The new cells travel to the bone marrow and gradually restart blood production over a few weeks. Donor transplants carry extra risks, including the donor’s immune cells reacting against the recipient’s body. Because it is a major treatment, doctors consider age and overall health when recommending it.
CAR-T therapy, which reprograms your immune cells, works well in some blood cancers that came back.29PubMed Central. CAR-T Cell Therapy in Hematological Malignancies: Current Opportunities and Challenges Blood cancer treatment also often lowers blood counts, so transfusions of red cells or platelets are common.30PubMed. Transfusion challenges in hematology oncology and hematopoietic stem cell transplant – Literature review and local experience
What to Expect at Your First Visit
Expect questions on symptoms, bleeding or clots, family history and medicines. The doctor usually asks when symptoms began, whether anything has changed, and whether you have had past bleeding, clots or transfusions. The physical exam may include feeling the neck, armpits and abdomen for swollen glands or an enlarged spleen, and looking at skin for bruises. Fresh blood work is often drawn the same day.
Bring earlier blood results and the referral letter, a full list of medicines and supplements, and any family history of blood disorders or cancer. Someone to take notes helps.
Good questions: What do you think is causing my results? What tests come next and when? Is this a cancer or non-cancer concern? Who do I call with new symptoms?
Leaving without a firm answer is common and does not mean something is being missed. Results often come at a follow-up, and you can ask to see them in a portal.