Leukaemia is a blood cancer. It affects the white blood cells, which are a really important part of our immune system that fights infection. Chronic lymphocytic leukaemia (CLL) is one of four main types of leukaemia.

There are four main types of leukaemia: acute myeloid leukaemia (AML), acute lymphoblastic leukaemia (ALL), chronic myeloid leukaemia (CML) and chronic lymphocytic leukaemia (CLL).

Different leukaemias are diagnosed according to the type of white blood cell affected and the speed with which the cancer progresses.

CLL is a chronic leukaemia meaning it develops slowly, often over many years. It affects a type of white blood cell called lymphoid cells.

Making blood

White blood cells are made in the bone marrow – the soft tissue in the middle of our bones where all our blood cells are made. Mother cells, called stem cells, reside here and make every type of blood cell that we need.

Stem cells constantly produce new blood cells to replace old and damaged ones. New cells only leave the bone marrow once they have fully matured. This process is well controlled so that we have just the right amount of each blood cell in our body.

Developing leukaemia

When someone has leukaemia, control of blood cell production breaks down. In the case of CLL the stem cells in the bone marrow make lots of mature lymphoid cells. Although these appear very similar to normal white blood cells, vital to a healthy immune system, these do not function in the same way. So people with CLL have an increased risk of infection.

The cancer cells cluster in the bone marrow and prevent other important blood cells from being made. Most of the problems of leukaemia are caused by the lack of normal cells in the blood, rather than the leukaemia cells themselves.

What are the signs and symptoms?