Chronic lymphocytic leukaemia

What is CLL?

Chronic lymphocytic leukaemia (CLL) is a type of leukaemia and therefore a type of blood cancer. The word ‘chronic’ in the name indicates that the disease may develop slowly. The word ‘lymphocytic’ refers to the type of blood cells affected which are called lymphocytes.

CLL is the most common leukaemia diagnosed in adults. CLL is very rarely diagnosed in children and young adults. Many people diagnosed with CLL report no symptoms and the diagnosis is often highlighted following a routine blood test for another condition.

Facts about chronic lymphocytic leukaemia

  • 40% of all new CLL cases in the UK are diagnosed in people aged 75 years or over.
  • CLL is the most common type of leukaemia diagnosed in adults – 38% of all leukaemia cases.
  • Over 3,803 people are diagnosed with CLL in the UK every year.

How does CLL develop?

CLL develops in white blood cells called lymphocytes in the bone marrow.

The bone marrow is the soft inner part of the bones, where new blood cells are produced. Every blood cell grows from a stem cell in the bone marrow. Normally, the stem cells make an early stage of the blood cell called a blast. These blasts should develop into normal healthy blood cells. In the case of lymphoblasts, these derive from lymphoid stem cells, and should develop into fully functioning lymphocytes. Lymphocytes have a vital role in the immune system and protect against infection.

Lymphoid cells are a type of white blood cell that help fight infection. A lymphoid stem cell becomes a lymphoblast cell and then one of three types of lymphocytes:

  • B lymphocytes that make antibodies to help fight infection.
  • T lymphocytes that help B lymphocytes make the antibodies that help fight infection.
  • Natural killer cells that attack cancer cells and viruses.

CLL occurs when a lymphoid cell develops changes/alterations (mutations) in its DNA. A cell’s DNA controls how a cell develops and functions, to multiply at a set rate and to die at a set time. A cell with altered DNA may be unable to fully develop and mature properly to fulfil its function to protect against infection. In addition, the usual controls for growth and dying may be lost, thereby allowing the resulting abnormal cells to continue to multiply quickly. The abnormal lymphocytes could now be called leukaemia cells or CLL cells.

The CLL cells may multiply and survive better than normal cells and over time, may accumulate in the blood, bone marrow, spleen and lymph nodes. In CLL, the bone marrow produces too many B lymphocytes which are not fully developed and could be called immature. These CLL cells are not able to fight infection very well. Also, as the number of CLL cells increases in the blood and bone marrow, there is less room for healthy white blood cells, red blood cells, and platelets.

However, there is variation in effect of CLLs with regards other blood cells. CLL cells do not always prevent normal blood cell production as extensively as leukaemia cells in people with acute leukemia. In some people with CLL, the disease progresses slowly and, if there are minimal changes in their blood cell counts, CLL may remain stable for years. Other people may have a faster-growing form of the disease, in which the CLL cells accumulate in the bone marrow and blood, and there is a significant decrease in the numbers of red blood cells and platelets.

Searching for answers: Leukaemia UK funded research

Dr Adam Linley: 2018 John Goldman Fellow whose project aimed to identify what causes resistance to therapy in CLL patients. Whilst therapies are available, none are curative, and some patients develop resistance and suffer relapse. Often the relapse results in a more aggressive disease.

Facts and statistics quoted on this page are derived from a number of sources which include: The Office of National Statistics (ONS), Cancer Research UK (CRUK), Haematological Malignancy Research Network (HMRN), Blood Cancer UK (BCUK), Lymphoma Action & Myeloma UK

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