Leukaemia is a cancer that begins in the blood-forming tissues of the body, especially the bone marrow, where blood cells are made. It causes the rapid growth of abnormal blood cells that can crowd out healthy cells, affecting the body’s ability to fight infection, carry oxygen, and form blood clots. Understanding leukaemia means recognising that this disease comes in several different forms, each with its own patterns, risks, and approaches to care.

What is Leukaemia?

Leukaemia is cancer that affects the blood cells in your body, particularly those made inside your bone marrow—the soft, spongy tissue found in the inner cavity of your bones. This is where most of your body’s blood is produced. When leukaemia develops, something goes wrong during the normal process of blood cell development^[1].

Normally, your bone marrow produces blood cells in an organised way. These cells go through several stages before they mature into three main types: red blood cells that carry oxygen throughout your body, white blood cells that help fight infections, and platelets that help your blood to clot when you are injured. If you have leukaemia, a single cell in your bone marrow undergoes a change in its DNA—a mutation—and begins to multiply uncontrollably^[1].

These abnormal cells, called leukaemia cells, are usually immature white blood cells that never fully develop. They cannot perform the normal functions that healthy white blood cells do. Instead of fighting infection, they simply multiply and take up space in your bone marrow. As they multiply, they crowd out the developing healthy blood cells, leaving less and less room for your body to make the red blood cells, healthy white blood cells, and platelets it needs^[1].

The word leukaemia itself comes from Greek words meaning “white” and “blood,” which reflects the fact that the disease often involves white blood cells^[1]. Unlike many other cancers, leukaemia does not usually form a solid mass or tumour that can be seen on imaging tests like X-rays or CT scans. Instead, the cancer cells circulate in the blood and bone marrow^[1].

Types of Leukaemia

There are four main types of leukaemia. Doctors classify them based on two factors: how quickly the disease progresses and which type of blood cell is affected^[3].

The first factor is speed. Acute leukaemia grows very quickly. The leukaemia cells divide rapidly, and the disease progresses fast. People with acute leukaemia often feel sick within weeks of the cancer cells forming. This type requires immediate treatment and is considered life-threatening^[1]. Chronic leukaemia, on the other hand, progresses more slowly. The cells divide at a slower rate, and the disease develops over months or even years. Some people with chronic leukaemia may not have symptoms for a long time^[3].

The second factor is the type of cell involved. Lymphocytic leukaemia (also called lymphoblastic leukaemia) develops when abnormal changes occur in lymphoid stem cells, which normally develop into white blood cells called lymphocytes. Myeloid leukaemia (also called myelogenous leukaemia) develops when abnormal changes occur in myeloid stem cells, which normally develop into red blood cells, platelets, or certain types of white blood cells^[8].

Combining these two factors gives us the four main types: acute lymphoblastic leukaemia (ALL), acute myeloid leukaemia (AML), chronic lymphocytic leukaemia (CLL), and chronic myeloid leukaemia (CML)^[3]. ALL is the most common type of cancer in children, while AML is the second most common childhood leukaemia. Among adults, AML and CLL are the two most common types^[3].

How Common is Leukaemia?

Leukaemia is the tenth most common cancer in the United States. According to recent estimates, there are about 61,000 new cases of leukaemia diagnosed each year in the United States, accounting for around three percent of all new cancer cases^[6]. Globally, approximately 474,519 new cases are diagnosed each year, with about 67,784 of those occurring in North America^[6].

Leukaemia occurs most often in adults older than 55 years of age. However, it is also the most common cancer diagnosed in children younger than 15^[4]. Among children and teens, acute lymphoblastic leukaemia accounts for about 75 percent of paediatric leukaemia cases^[3]. Among adults, chronic lymphocytic leukaemia makes up about 35 percent of cases, and acute myeloid leukaemia accounts for about 32 percent^[13].

Survival rates vary widely depending on the type of leukaemia. The current five-year relative survival rate ranges from 27 percent for adults diagnosed with acute myeloid leukaemia to 86 percent for those with chronic lymphocytic leukaemia. For children, adolescents, and young adults, the five-year survival rate ranges from 66 percent for those with AML to 92 percent for those with ALL^[13].

Causes of Leukaemia

Leukaemia begins when the DNA inside a blood cell in your bone marrow changes or mutates. This mutation causes the cell to lose its ability to develop and function normally. While researchers understand how leukaemia starts, the exact cause of these DNA changes remains largely unknown^[1][7].

The mutation causes the affected cell to multiply out of control. These abnormal cells do not die off when they should, as healthy cells do. Instead, they accumulate and begin to take over the space inside the bone marrow, crowding out cells that are trying to develop into healthy red blood cells, white blood cells, and platelets^[1].

Because fewer healthy blood cells are produced and released into the bloodstream, your body’s organs and tissues do not get the oxygen they need to work properly. Your body also loses its ability to fight infections effectively or to form blood clots when needed^[1].

Risk Factors for Leukaemia

Although the cause of leukaemia is not fully understood, experts have identified several factors that can increase a person’s risk of developing the disease^[3].

One important risk factor is age. Your risk of developing leukaemia increases as you get older, and it is most common in people over the age of 60^[7].

Certain genetic conditions can increase the risk of leukaemia. These include Down syndrome, Klinefelter syndrome, ataxia telangiectasia, and Bloom syndrome. Other genetic conditions that affect the body’s ability to repair DNA, such as Fanconi anaemia and dyskeratosis congenita, also raise the risk. In addition, people with mutations in specific genes, such as RUNX1 or CEBPA, may have a higher chance of developing leukaemia^[6].

Exposure to high levels of radiation is a known risk factor. This includes exposure to ionizing radiation from nuclear accidents or radiation therapy used to treat other cancers^[3][6]. People who have undergone chemotherapy with certain drugs, particularly alkylating agents or topoisomerase II inhibitors, also have an increased risk of developing leukaemia later on^[6].

Environmental factors can also play a role. Repeated exposure to certain chemicals, especially benzene and toluene, which are found in solvents and some industrial settings, has been linked to leukaemia^[3][6]. Smoking is another environmental risk factor^[6].

Certain viral infections have been associated with leukaemia. These include the Epstein-Barr virus and the human T-lymphotropic virus^[6]. In addition, people with a strong family history of leukaemia may be at higher risk, although leukaemia is not typically considered a hereditary disease in the same way some other cancers are^[3].

Symptoms of Leukaemia

The symptoms of leukaemia vary depending on the type and stage of the disease. Some people, particularly those with chronic leukaemia, may not have any symptoms at first. Sometimes leukaemia is discovered during blood tests that are done for another reason^[2].

Common symptoms include feeling persistently tired or weak. This happens because your body does not have enough healthy red blood cells to carry oxygen to your tissues and organs^[2]. Many people experience frequent or severe infections because the abnormal white blood cells cannot fight off bacteria and viruses effectively^[2].

You may notice that you bruise or bleed more easily than usual. This occurs because your bone marrow is not producing enough platelets, the cells that help your blood clot. Some people have recurrent nosebleeds or notice tiny red spots on their skin, called petechiae, which are caused by bleeding under the skin^[2][7].

Fever or chills that come and go, often resembling flu-like symptoms, are common. You might also experience night sweats that are severe enough to soak your clothes or bedding^[2][3]. Many people with leukaemia lose weight without trying to, and they may also lose their appetite^[2].

Swollen lymph nodes, which are small glands that are part of your immune system, may appear in your neck, armpits, or groin. Your liver or spleen may also become enlarged, which can cause discomfort or a feeling of fullness in your abdomen^[2][3]. Bone pain or tenderness is another symptom that some people experience^[2].

Other symptoms might include headaches, a sore mouth or mouth ulcers (called mucositis), swollen or bleeding gums, and a general sense of not feeling well^[3][14].

It is important to note that these symptoms are often vague and can be similar to those of the flu or other common illnesses. Many people overlook early symptoms because they do not seem serious. However, if you have any persistent signs or symptoms that worry you, it is important to see a doctor^[2].

How is Leukaemia Diagnosed?

If your doctor suspects you may have leukaemia, they will perform several tests to confirm the diagnosis and determine what type of leukaemia you have^[7].

The first step is usually a physical examination. Your doctor will look for physical signs of leukaemia, such as pale skin from anaemia (a condition where you do not have enough red blood cells), swelling of your lymph nodes, and an enlarged liver or spleen^[10].

Blood tests are a key part of the diagnosis. A complete blood count (CBC) is a test that measures the levels of different types of cells in your blood. If you have leukaemia, this test may reveal abnormal levels of white blood cells and abnormally low counts of red blood cells or platelets. In some cases, leukaemia cells can be seen in the blood sample itself^[3][10].

To confirm the diagnosis, doctors usually need to examine your bone marrow. There are two main types of bone marrow tests: bone marrow aspiration and bone marrow biopsy. Both involve removing a sample of bone marrow and bone, usually from a spot in the back of your hip bone. The samples are sent to a laboratory where specialists look at the cells under a microscope to check for leukaemia cells and determine which type of leukaemia you have^[7][10].

Additional tests may be performed to learn more about the characteristics of the leukaemia cells. These can include genetic tests to look for specific gene and chromosome changes, which can help doctors predict how the disease will behave and which treatments might work best^[7][10].

If leukaemia is confirmed, your doctor may order imaging tests or a lumbar puncture (also called a spinal tap) to check whether the cancer has spread to other parts of your body, such as your brain or spinal cord^[7].

Prevention of Leukaemia

Because the exact causes of leukaemia remain unknown, there is no certain way to prevent the disease. However, there are some steps you can take that may reduce your risk or help with early detection^[3].

One important measure is to avoid exposure to known risk factors when possible. This means limiting your exposure to high levels of radiation and avoiding repeated contact with chemicals such as benzene and toluene. If you work in an environment where these chemicals are present, make sure to follow safety guidelines and use protective equipment^[3].

If you smoke, quitting can reduce your risk not only of leukaemia but also of many other cancers and health problems. Smoking has been linked to an increased risk of developing leukaemia^[6].

Being aware of your family medical history is also important. If leukaemia or other blood disorders run in your family, share this information with your doctor. This can help them monitor your health more closely and be alert to any early signs of the disease^[3].

Regular medical check-ups can also be helpful. While there is no specific screening test for leukaemia in the general population, routine blood tests done for other reasons can sometimes detect abnormal blood cell counts that may lead to an early diagnosis^[2].

How Leukaemia Affects the Body

Leukaemia disrupts the normal functioning of your blood and bone marrow in several important ways. Understanding these changes can help explain why the disease causes the symptoms it does^[1].

The most fundamental problem is that leukaemia cells serve no useful purpose in keeping you healthy. Unlike normal white blood cells, which fight infections, leukaemia cells cannot perform this function. They simply take up space and consume resources that your body needs to produce healthy blood cells^[1].

As leukaemia cells multiply, normal blood cells have very little space and support to mature and multiply inside your bone marrow. This is because the leukaemia cells crowd them out. As a result, fewer and fewer healthy red blood cells, white blood cells, and platelets are made and released into your bloodstream^[1].

When you do not have enough red blood cells, your organs and tissues do not receive the oxygen they need to function properly. This can leave you feeling tired, weak, and short of breath. Without enough healthy white blood cells, your body cannot fight off infections as it normally would, making you more vulnerable to bacteria, viruses, and other germs^[1].

A shortage of platelets means your blood cannot clot properly. This is why people with leukaemia often bruise easily, have frequent nosebleeds, or notice small red spots on their skin where tiny blood vessels have bled under the surface^[1].

In some cases, large numbers of leukaemia cells can build up in certain parts of the body, such as the lymph nodes, liver, or spleen. This can cause these organs to swell, leading to discomfort or pain. If leukaemia cells spread to the brain or spinal cord, they can cause headaches, confusion, or other neurological symptoms^[2].