• CLL is one the four major leukaemia that affect adults. Incidences and numbers of patients diagnosed with these leukaemia in the United Kingdom (UK) are shown in Table 1.

Table 1           Main leukaemia and their incidences in the UK (2016-2018)1

Leukaemia type in adults Incidence per 100,000 people No of UK patients affected per year
Acute lymphoblastic leukaemia (ALL) 1.1 791
Acute myeloid leukaemia (AML) 4.9 3089
Chronic lymphocytic leukaemia (CLL) 6.2 3803
Chronic myeloid leukaemia (CML) 1.3 829

1 Cancer Research UK, Accessed: December 2021

  • CLL is a type of blood cancer that occurs when the body makes too many abnormal lymphocyte white blood cells.
  • Normally, healthy lymphocytes help the body fight infection and disease. In CLL, the lymphocytes become abnormal and do not function or die. These are known as leukaemia cells. They are present in the bone marrow, lymph nodes, spleen, liver and other organs. Lymph nodes are small glands that are part of the lymphatic system.
  • The function of lymphocytes is to recognise bacteria, viruses and toxins, produce antibodies to them and destroy them. As CLL patients have an impaired immune system, they are at greater risk of infections.
  • In a normal bone marrow, the immature lymphocytes mature into three different types of lymphocyte (Figure 1). These are:
  • B-lymphocytes (or B-cells) that make antibodies to help fight infection.
  • T-lymphocytes (or T-cells) that destroy invading organisms and cells that have become cancerous.
  • Natural killer cells (NK‑cells) that attack cancer cells and viruses.

Figure 1         Development of stem cells in the bone marrow

Source: Leukaemia Care

  • CLL usually affects older people, with an average age at diagnosis of 72. It is very rare in children.
  • It affects nearly twice as many men as women.
  • CLL is also more common in White people than in people from Asian, African or Hispanic backgrounds.
  • The term ‘chronic’ in CLL indicates that CLL usually develops slowly over months or years. However, in a few cases, CLL progresses more rapidly, in which case immediate treatment is required.
  • When the leukaemia cells are only in the lymph nodes, the condition is known as small lymphocytic lymphoma (SLL). CLL and SLL are different forms of the same disease, but they both respond to the same treatment.