Chronic lymphocytic leukaemia is a type of blood cancer that develops slowly, affecting white blood cells that normally help fight infections. Many people live with this condition for years, and some may never need treatment at all.
What Is Chronic Lymphocytic Leukaemia?
Chronic lymphocytic leukaemia, often shortened to CLL, is a cancer that starts in the blood and bone marrow. The bone marrow is the soft, spongy tissue inside bones where blood cells are made. In CLL, something goes wrong with the way certain white blood cells develop.[1]
Normally, your bone marrow produces healthy white blood cells called lymphocytes, which are part of your body’s defence system against infections. In CLL, these lymphocytes don’t develop properly. They become abnormal and start to multiply out of control. These faulty cells crowd out the healthy blood cells, including red blood cells that carry oxygen and platelets that help your blood clot when you’re injured.[2]
The word “chronic” in the name tells us something important about this disease. It means that CLL usually progresses very slowly, taking months or even years before symptoms appear. This is different from other types of leukaemia that grow quickly and require immediate treatment. The term “lymphocytic” refers to the type of cells affected, which are the lymphocytes.[3]
There are different types of lymphocytes in your body. Most people with CLL have the disease in their B-cells, which are white blood cells that make antibodies. Antibodies are proteins that recognise and help destroy germs and other harmful invaders. Nearly all CLL cases involve B-cells, though there is a related condition affecting T-cells, another type of lymphocyte that helps control your immune response.[3]
How Common Is Chronic Lymphocytic Leukaemia?
Chronic lymphocytic leukaemia is one of the most common types of leukaemia in adults, particularly in Western countries. In the United States, it represents about 25 to 30 percent of all leukaemia cases. Medical experts estimate that approximately 18,700 people will be diagnosed with CLL each year, and about 4,460 deaths occur annually from this condition.[3][4]
The disease affects about 5 in every 100,000 people in the United States. While this might sound like a large number, it’s less common than some other cancers. For comparison, lung cancer, one of the most frequently diagnosed cancers, affects more than 238,000 people each year in the same country.[3]
CLL has clear patterns in who it affects. It is more common in older adults, with most people being around 71 years old when they receive their diagnosis. The condition typically affects people aged 65 and older, though it can occur in people as young as 30. It rarely affects children. Men are more likely to develop CLL than women. The disease is also more common in white people compared to people from other racial or ethnic backgrounds.[3][7]
What Causes Chronic Lymphocytic Leukaemia?
Scientists don’t fully understand what triggers chronic lymphocytic leukaemia. The disease happens when certain chromosomes and genes inside blood cells change or mutate during a person’s lifetime. These changes occur in the genetic material, or DNA, within bone marrow cells. However, researchers haven’t identified exactly what causes these mutations to happen in the first place.[3][4]
What doctors do know is that CLL is not caused by anything a person did or didn’t do. It’s not contagious, meaning you can’t catch it from another person. The genetic changes that lead to CLL happen randomly during life, rather than being something people are born with. These changes affect how lymphocytes grow and multiply, causing them to become cancerous cells that don’t function properly.[4]
Some research suggests that genetic factors play a larger role than environmental factors in causing CLL. Studies have looked at whether exposure to certain chemicals, radiation, or other environmental hazards might increase risk, but the evidence is not strong. Unlike some other types of leukaemia that have been linked to radiation exposure, such as in atomic bomb survivors, CLL does not show the same pattern.[4]
Risk Factors for Developing CLL
Although the exact cause of chronic lymphocytic leukaemia remains unknown, researchers have identified several factors that may increase a person’s chances of developing this condition. Understanding these risk factors can help people be more aware of their health, though having one or more risk factors doesn’t mean someone will definitely develop CLL.[3]
Age is one of the strongest risk factors. The likelihood of developing CLL increases significantly as people get older. The average age at diagnosis is 71 years, and most cases occur in people over 65. This means that older adults should be particularly attentive to any unusual symptoms, though younger people can also develop the condition starting from around age 30.[3]
Family history plays an important role. People who have close biological relatives with CLL, such as a parent, sibling, or child with the disease, are two to four times more likely to develop it themselves. This suggests that inherited genetic factors may make some families more susceptible to CLL, even though the disease itself is not directly passed from parent to child.[3]
Being male increases the risk of CLL. Men are more likely than women to develop this type of leukaemia, though doctors don’t fully understand why this difference exists. Race and ethnicity also matter: white people have higher rates of CLL compared to people from other racial or ethnic backgrounds.[3][8]
Certain environmental and occupational exposures have been studied as possible risk factors. Veterans who were exposed to Agent Orange, a chemical herbicide used during the Vietnam War, show increased rates of CLL. The United States Veterans Affairs recognises this connection. Some research has also suggested that people working in certain industries, such as farmers working around rubber manufacturing or workers exposed to benzene and heavy solvents, may have higher risk. However, these associations need more research to be confirmed. People who work with uranium and are exposed to ionizing and non-ionizing radiation may also have increased risk.[4]
There is evidence linking tobacco use and cigarette smoking to an elevated risk of CLL. People who smoke show a significantly higher chance of developing this leukaemia compared to those who don’t use tobacco products.[4]
A condition called monoclonal B-cell lymphocytosis, or MBL, increases CLL risk. In this condition, a person has a higher than normal number of identical B-cells in their blood, but not enough to be diagnosed with CLL. People with MBL may go on to develop full CLL, though not everyone with this condition progresses to leukaemia.[3]
Symptoms of Chronic Lymphocytic Leukaemia
One of the most distinctive features of chronic lymphocytic leukaemia is that many people have no symptoms at all when they’re first diagnosed. Because CLL develops so slowly, it can be present for months or even years before causing any noticeable problems. In fact, most people learn they have CLL after having routine blood tests during regular physical examinations, not because they felt unwell.[2][7]
When symptoms do appear, they develop gradually as the disease progresses. One of the most common signs is swollen lymph nodes. These might feel like painless lumps under the skin, most often in the neck, armpit, or groin. Some people also notice swelling in the stomach area. The lymph nodes are part of the body’s immune system and can become enlarged when filled with cancerous lymphocytes.[2][7]
Fatigue is another frequent symptom. This tiredness happens because CLL affects red blood cells, leading to anaemia, a condition where you don’t have enough healthy red blood cells to carry oxygen throughout your body. People with anaemia often feel persistently tired and weak, even after resting. This exhaustion can interfere with daily activities and quality of life.[3][7]
Many people with CLL experience frequent infections. Because the disease affects white blood cells that normally fight germs, the immune system doesn’t work as well as it should. These infections might not respond to treatment as quickly as expected, and new infections may develop frequently. Fever often accompanies these infections.[2][3]
Night sweats are common in CLL. These aren’t just ordinary sweating from being too warm at night. People describe them as drenching sweats that soak through nightclothes and bedding, requiring them to change clothes or sheets during the night. This symptom can be particularly disruptive to sleep and daily life.[2][7]
Unexplained weight loss can occur as CLL progresses. People may lose weight without trying, meaning they haven’t changed their diet or increased their physical activity. Along with weight loss, some people notice a decreased appetite and simply don’t feel like eating.[2][7]
Some people feel pain or a sense of fullness in the upper left part of the belly, just below the ribs. This happens when CLL causes the spleen to enlarge. The spleen is an organ that filters blood and is part of the immune system. When cancerous white blood cells accumulate there, it can grow larger than normal and cause discomfort. Similarly, an enlarged liver can cause pain on the right side.[2][3]
Easy bruising or bleeding can develop as CLL progresses. This occurs when the disease affects platelets, the blood cells responsible for clotting. Some people notice small, flat, dark-red spots under the skin called petechiae, which are caused by bleeding under the skin’s surface.[7]
How Can You Prevent Chronic Lymphocytic Leukaemia?
Unfortunately, there is no known way to prevent chronic lymphocytic leukaemia. Because scientists haven’t identified a specific cause for the disease, and because it results from genetic changes that happen randomly during a person’s lifetime, there are no proven prevention strategies. This differs from some other cancers where lifestyle changes, such as not smoking or maintaining a healthy weight, can reduce risk.[8]
The genetic mutations that lead to CLL occur in cells during adulthood, not at birth. These changes are not passed directly from parents to children, though family history does increase risk. Since these mutations happen unpredictably, medical science hasn’t yet found ways to stop them from occurring.[3]
For people with known risk factors, such as those with a family history of CLL or those who have been exposed to Agent Orange, there are no special screening tests or preventive measures recommended. The best approach is to attend regular check-ups with your doctor and report any unusual symptoms promptly. Early detection through routine blood tests can help doctors monitor the condition and start treatment when necessary.[4]
While you can’t prevent CLL itself, maintaining overall good health is always beneficial. This includes eating a balanced diet, staying physically active, not smoking, limiting alcohol consumption, and managing stress. These healthy habits support your immune system and overall well-being, which becomes especially important if you do develop CLL or any other health condition.[16]
How the Disease Affects Your Body
To understand how chronic lymphocytic leukaemia affects the body, it helps to know how blood cells normally develop. Your bone marrow continuously produces blood stem cells, which are immature cells that eventually become mature blood cells. These stem cells can develop into different types of blood cells depending on what your body needs.[7]
There are two main pathways for blood cell development. One leads to myeloid cells, which become red blood cells that carry oxygen, platelets that help blood clot, or certain white blood cells called granulocytes that fight infection. The other pathway leads to lymphoid cells, which become lymphocytes: B cells, T cells, or natural killer cells. All of these lymphocytes play different roles in your immune system.[7]
In chronic lymphocytic leukaemia, something goes wrong during this development process. Too many blood stem cells turn into abnormal lymphocytes instead of healthy ones. These abnormal cells are sometimes called leukaemia cells. They look similar to normal lymphocytes under a microscope, which is why CLL is described as involving “morphologically mature” cells. However, despite their mature appearance, they don’t function properly.[4][7]
The leukaemia cells can’t fight infections effectively like healthy white blood cells should. Even worse, they live much longer than normal lymphocytes and keep multiplying. As their numbers increase in the blood and bone marrow, they take up space that healthy cells need. This crowding effect means there’s less room for the bone marrow to produce normal red blood cells, healthy white blood cells, and platelets.[7]
This displacement of healthy cells leads to several problems. When red blood cell production decreases, anaemia develops, causing fatigue and weakness because your body’s tissues don’t get enough oxygen. When platelet numbers drop, you may bruise easily or experience bleeding problems because your blood doesn’t clot properly. When healthy white blood cells are crowded out, your immune system weakens, making you more susceptible to infections.[7]
The abnormal lymphocytes don’t just stay in the bone marrow and blood. They can travel to and accumulate in lymph nodes throughout the body, causing them to swell. The lymph nodes in the neck, armpits, and groin are commonly affected. The cancerous cells can also collect in the spleen and liver, making these organs enlarge. An enlarged spleen or liver can cause discomfort and a feeling of fullness in the abdomen.[4][14]
CLL can also cause immune system problems beyond just having fewer working white blood cells. Some people develop autoimmune complications, where the immune system mistakenly attacks the body’s own healthy cells. This can lead to autoimmune haemolytic anaemia, where red blood cells are destroyed, or immune thrombocytopenia, where platelets are destroyed. The body may also produce lower levels of immunoglobulins, the proteins that help fight infections, making people even more vulnerable to getting sick.[14]
The disease progresses through stages. In early stages, you might just have elevated lymphocyte counts in blood tests without any symptoms or swollen lymph nodes. As it advances, lymph nodes may enlarge, followed by enlargement of the spleen and liver. In later stages, anaemia and low platelet counts develop. This progression usually happens slowly over years, which is why many people can live with CLL for a long time, sometimes without needing treatment immediately.[4]
