Yes, leukemia is cancer of the blood. More precisely, it starts in the bone marrow, the spongy tissue inside your bones where blood cells are made. In leukemia, genetic mutations cause certain blood cells to grow and divide out of control, eventually crowding out the healthy cells your body needs to function. The overall five-year survival rate for leukemia is about 68.6%, though this varies widely depending on the type.
How Leukemia Disrupts Blood Cell Production
Your bone marrow constantly produces three types of blood cells: red blood cells that carry oxygen, white blood cells that fight infection, and platelets that help your blood clot. In a healthy body, these cells mature, do their job, and die on schedule to make room for new ones.
In leukemia, mutations tell certain blood cells to keep growing and dividing instead of maturing normally or dying when they should. Over time, these abnormal cells accumulate in the bone marrow and spill into the bloodstream. As they build up, they crowd out the healthy red blood cells, white blood cells, and platelets. That crowding effect is what drives most of the symptoms people experience: not enough red blood cells means fatigue, not enough functional white blood cells means frequent infections, and not enough platelets means easy bleeding and bruising.
The Four Main Types
Leukemia is classified along two axes: which type of white blood cell is affected, and how fast the disease progresses. This creates four main categories.
The first distinction is the cell type. Lymphocytic leukemias develop from cells that would normally become lymphocytes, a family of immune cells that includes T cells and B cells. Myeloid leukemias develop from cells that would normally become granulocytes and monocytes, different types of white blood cells involved in fighting bacteria and clearing debris.
The second distinction is speed. Acute leukemias develop rapidly. The cancerous cells are immature and completely unable to perform normal immune functions, which is why acute forms can become life-threatening quickly without treatment. Chronic leukemias develop in more mature cells that can still partially do their jobs, so the disease progresses more slowly, sometimes over years.
Combining these two axes gives you the four types:
- Acute lymphocytic leukemia (ALL), the most common childhood leukemia, involves rapidly multiplying immature lymphocytes.
- Acute myeloid leukemia (AML), more common in adults, involves rapidly multiplying immature myeloid cells.
- Chronic lymphocytic leukemia (CLL), the most common leukemia in adults overall, progresses slowly and may not need treatment right away.
- Chronic myeloid leukemia (CML), a slower-growing myeloid cancer that often responds well to targeted treatments.
Common Symptoms
Because leukemia disrupts the production of all three major blood cell types, its symptoms are wide-ranging. Many of them mimic common illnesses, which is one reason leukemia can go undetected early on.
The most frequently reported signs include persistent fatigue and weakness (from low red blood cells), frequent or severe infections (from dysfunctional white blood cells), and easy bleeding or bruising, recurrent nosebleeds, or tiny red spots on the skin called petechiae (from low platelets). Other symptoms include fever or chills, unexplained weight loss, swollen lymph nodes, an enlarged liver or spleen, excessive night sweats, and bone pain or tenderness.
Acute forms tend to produce symptoms suddenly and severely. Chronic forms may cause mild or no symptoms for months or even years, sometimes turning up only through a routine blood test.
What Causes It
Leukemia begins with genetic mutations in blood-forming cells in the bone marrow. In most cases, no single cause can be pinpointed. The mutations tell the cell to keep dividing when it normally would stop, and over time, these defective cells accumulate.
Known risk factors include previous cancer treatment with certain chemotherapy drugs or radiation, prolonged exposure to industrial chemicals like benzene, smoking, certain genetic conditions such as Down syndrome, and a family history of leukemia. Some forms involve a specific chromosomal abnormality, like the Philadelphia chromosome commonly found in CML, where two chromosomes swap segments and create a protein that drives uncontrolled cell growth. But many people who develop leukemia have no identifiable risk factors at all.
Leukemia vs. Other Blood Cancers
Leukemia is not the only cancer that affects the blood. Lymphoma and multiple myeloma are also blood cancers, but they involve different cells and behave differently.
Leukemia primarily affects white blood cells in the bone marrow and bloodstream. Lymphoma is a cancer of the lymphatic system, developing in the lymph nodes, spleen, or bone marrow from lymphocytes that have already left the marrow. Multiple myeloma targets plasma cells, a specialized type of white blood cell responsible for producing antibodies. In myeloma, cancerous plasma cells accumulate in the bone marrow and produce abnormal antibodies instead of the ones your immune system actually needs.
The distinction matters because treatment strategies, progression patterns, and prognoses differ significantly across these three categories.
How Leukemia Is Treated
Treatment depends heavily on the type of leukemia, how fast it’s progressing, and the patient’s age and overall health. The main approaches include chemotherapy to kill cancer cells, targeted therapy that zeroes in on specific molecular abnormalities driving the cancer, and stem cell transplants.
In a stem cell transplant, high-dose chemotherapy (and sometimes radiation) is used to destroy the diseased bone marrow, followed by an infusion of healthy donor stem cells that rebuild the blood-forming system from scratch. This is the most intensive option and is typically reserved for aggressive or relapsed cases. Targeted therapies have transformed the outlook for certain types, particularly CML, where drugs that block the abnormal protein produced by the Philadelphia chromosome can keep the disease under control for decades.
Biomarker testing is increasingly part of the treatment process. By analyzing the specific genetic changes in your leukemia cells, doctors can predict which targeted drugs are most likely to work for your particular case. For chronic leukemias caught early, treatment may not begin immediately. Instead, doctors monitor bloodwork at regular intervals and start treatment only when the disease shows signs of progressing, an approach called watchful waiting.