What is Leukemia? Types, Symptoms and Treatment

Leukemia is one of the more commonly discussed blood cancers, partly because it affects people of all ages, from young children to older adults, though different types tend to occur at different life stages. Understanding what leukemia actually is, and how its main types differ, makes it easier to understand a diagnosis, ask informed questions, and know what to expect from the treatment process.

Bone marrow, the soft tissue inside your bones, is where blood cells are made: red cells that carry oxygen, white cells that fight infection, and platelets that help blood clot. In leukemia, a genetic change occurs in an early blood-forming cell, causing it to divide uncontrollably and produce abnormal or immature white cells. These abnormal cells accumulate in the marrow and bloodstream, crowding out the production of normal, healthy blood cells.

This crowding-out effect explains most of leukemia's symptoms. Fewer normal red cells means anemia and fatigue. Fewer normal, functional white cells means a higher risk of infection, even though the total white cell count on a blood test may actually look high because of the abnormal cells. Fewer platelets means easier bruising and bleeding.

Leukemia is classified along two axes. The first is speed: acute leukemias develop and progress quickly, over days to weeks, and generally need prompt treatment. Chronic leukemias develop more slowly, sometimes over months to years, and are occasionally found incidentally on a routine blood test before symptoms appear.

The second axis is which cell line is affected: myeloid or lymphoid. Combining these gives four broad types. Acute lymphoblastic leukemia (ALL) is more common in children but also occurs in adults. Acute myeloid leukemia (AML) is seen more often in adults and progresses quickly. Chronic lymphocytic leukemia (CLL) typically affects older adults and often progresses slowly. Chronic myeloid leukemia (CML) is strongly associated with a specific genetic change called the Philadelphia chromosome and today is often well managed with oral targeted therapy.

Symptoms often reflect low blood counts: persistent fatigue and weakness, frequent or recurrent infections, easy bruising or bleeding from the gums or nose, tiny red or purple skin spots called petechiae, unexplained fever or night sweats, bone or joint pain, and swollen lymph nodes. Chronic leukemias can also be entirely symptom-free in early stages and picked up only through a routine blood count.

Diagnosis usually starts with a complete blood count and a peripheral blood smear, which can reveal abnormal or immature cells. Confirming the exact subtype, which is essential for choosing treatment, typically requires a bone marrow biopsy along with immunophenotyping (identifying markers on the surface of the abnormal cells) and, increasingly, genetic or molecular testing to look for specific mutations such as the Philadelphia chromosome in CML or FLT3 and NPM1 mutations in AML.

Treatment is guided by the specific type and risk category rather than a one-size-fits-all protocol. Chemotherapy remains a backbone of treatment for acute leukemias, aiming to bring the disease into remission. Targeted oral therapies, such as tyrosine kinase inhibitors, have changed the outlook for CML, allowing many patients to manage the disease with daily medication and monitoring. For CLL, treatment may not be needed immediately and can range from watchful waiting to targeted therapy depending on disease progression. In select cases of acute leukemia, a bone marrow transplant may be recommended, particularly when the disease carries higher-risk features or after initial treatment.

Because leukemia is not a single disease, outcomes and treatment plans vary considerably by subtype, genetic features, and individual health. A clinical haematologist tailors the plan after full diagnostic workup, and many patients respond well to treatment, though the course and outlook differ from person to person.