Leukemia is a broad term for blood cancers that start in the blood and bone marrow, most often the white blood cells. It causes too many abnormal white blood cells, and interferes with your bone marrow’s ability to make red blood cells and platelets.

Five-year Leukemia survival rates

Overview and types

There are several types of leukemia, categorized based on whether it occurs in children or adults, if it is fast growing (acute) or slow growing (chronic), and if it starts in myeloid cells or lymphoid cells. The type determines the treatment options, so a proper diagnosis is critical.

Main leukemia types

Acute lymphocytic (or lymphoblastic) leukemia (ALL). Starts in the bone marrow where blood cells are made; more common in children.

Acute myeloid leukemia, acute myelocytic leukemia, acute myelogenous leukemia, acute granulocytic leukemia or acute non-lymphocytic leukemia (AML). Most common in older adults.

Chronic lymphocytic leukemia (CLL). Starts in lymphocytes in the bone marrow; mainly affects older adults and accounts for about one-third of all leukemias.

Chronic myeloid leukemia or chronic myelogenous leukemia (CML). Starts in blood-forming cells of bone marrow and invades the blood.

Chronic myelomonocytic leukemia (CMML). Starts in blood-forming cells of bone marrow and invades the blood; affects mainly older adults.

Hairy cell leukemia. Slow growing; some patients go years without symptoms or needing treatment.

Childhood leukemia. The most common cancer in children and teens, accounting for almost a third of all cancers. Most childhood leukemias are either ALL or AML; chronic leukemias are rare in children.

Causes of leukemia

DNA in normal bone marrow cells can cause them to become leukemia cells. DNA determines our genes, which are passed on from our parents. The genes that help cells grow, divide and stay alive are oncogenes. Genes that keep cell growth and division under control, or make cells die at the right time, are tumor suppressor genes. Any mutation in the chromosomes of these genes can lead to cancer.

The most common type of chromosome mutation that can lead to leukemia is a translocation, where DNA from one chromosome breaks off and attaches to a different chromosome. This affects nearby genes, like turning on oncogenes or turning off tumor suppressor genes.

Even though we inherit genes, the DNA mutations leading to leukemia can also be acquired during a lifetime. We know that exposure to radiation or cancer-causing chemicals can cause mutations.

However, in many cases, gene changes just happen inside a cell, without having an outside cause. These changes can build up as we age, which is why some forms of leukemia happen in older adults.