Leukaemia is a cancer of the blood, characterized by the rapid growth of abnormal blood cells in your bone marrow. Leukaemia usually involves the white blood cells which are normally potent infection fighters. In people with leukaemia, the bone marrow produces too many abnormal white blood cells, which do not function properly.
Leukaemia is classified based on how quickly it progresses, and the type of blood cell involved. There are many types of leukaemia with some being more common in children than adults.
Classification is based on two criteria, namely:
- The speed of disease progression, and
- Cell type
Classification Based On Speed Of Disease Progression
Acute leukaemia is the most common cancer in children with symptoms normally presenting at an early stage. It progresses rapidly and is life-threatening and, therefore, requires immediate treatment.
Chronic leukaemia is more common in adults than in children. It progresses more slowly than acute leukaemia, displaying few symptoms for many years. With this type of leukaemia, the leukaemia cells can still function in a sub-optimal manner.
Classification Based On Cell Type
Myelogenous Or Myeloid Leukaemia
This type of cancer develops from myeloid cells. Healthy myeloid cells develop into red blood cells, white blood cells and platelets.
Lymphocytic leukaemia (also known as lymphoid or lymphoblastic leukaemia) develops in the white blood cells (lymphocytes) in the bone marrow.
Healthy lymphoid cells develop into white blood cells that are an important part of your body’s infection-fighting immune system.
What Types Of Leukaemia Can You Get?
There are four main types of leukaemia, based on whether they are acute or chronic, and myeloid or lymphocytic. These include:
- Acute myeloid (or myelogenous) leukaemia (AML)
- Chronic myeloid (or myelogenous) leukaemia (CML)
- Acute lymphocytic (or lymphoblastic) leukaemia (ALL)
- Chronic lymphocytic leukaemia (CLL)
Acute Lymphocytic Leukaemia (ALL)
ALL is the most common type of leukaemia in children, teens and young adults under 40.
This leukaemia develops when DNA changes (mutations) cause the bone marrow to produce too many abnormal lymphocytes (white blood cells). It progresses quickly, replacing healthy cells, that produce lymphocytes, with leukaemia cells that cannot mature properly.
The abnormal lymphocytes produced in people with ALL are unable to fight infections properly. The abundance of these abnormal cells also reduces the space in the bone marrow for other healthy blood cells to develop.
Acute Myelogenous Leukaemia (AML)
AML is the most common type of acute leukaemia in adults. It mostly affects those over 65 although it occasionally occurs in children.
It is a fast-growing form of cancer of the blood which causes the bone marrow to overproduce abnormal white blood cells which crowd out healthy blood cells and affect the body’s ability to fight infections.
Chronic Lymphocytic Leukaemia (CLL)
CLL is a slow-growing cancer, accounting for about 25% of all cases of leukaemia. It is the most common chronic leukaemia in adults, especially those over 65. Symptoms often do not appear for several years.
CLL begins in lymphocytes in the bone marrow and then spreads into the blood and sometimes also into the lymph nodes and organs, such as the liver and spleen.
Chronic Myelogenous Leukaemia (CML)
CML is a slow-growing leukaemia that accounts for about 15% of leukaemias. It is more common in adults over 65 but can affect adults of any age. It rarely occurs in children.
CML is cancer that starts in the blood-forming myeloid cells or stem cells in your bone marrow.
Rare Types Of Leukaemia
There are many different types of leukaemia, with some being less common than others. Rare types of leukaemia include:
- Prolymphocytic leukaemia (PLL)
- Large granular lymphocytic (LGL
- Hairy cell leukaemia (HCL)
- Myelodysplastic syndromes (MDS)
Prolymphocytic Leukaemia (PLL)
PLL is very rare and accounts for less than 1% of chronic leukaemias. It is an aggressive type of leukaemia characterised by an excessive growth of immature lymphocytes.
PLL may develop alongside chronic lymphocytic leukaemia (CLL) or on its own, but it usually progresses faster than typical CLL. Although PLL tends to respond well to treatment, relapse is common.
Large Granular Lymphocytic (LGL)
LGL leukaemia is a chronic type of leukaemia that causes the body to produce abnormally large lymphocytes. People with autoimmune diseases may be more at risk of developing LGL.
LGL starts in the white blood cells, which are also called cytotoxic T-cells or natural killer cells. Two types of LGL occur, namely T-cell large granular lymphocytic leukaemia (T-LGL) and chronic lymphoproliferative disorder of NK-cells (CLPD-NK). Both types of LGL grow slowly and usually affect people over 60.
Hairy Cell Leukaemia (HCL)
HCL is a very rare subtype of chronic lymphocytic leukaemia (CLL) with only around 240 people being diagnosed with it each year in the UK. It typically develops in middle-aged men and progresses slowly. The word “hairy” describes the look of the cells which appear to have thin, hair-like outgrowths.
HCL occurs when bone marrow makes too many B cells (lymphocytes). These are a type of white blood cell that fights infection. As the number of leukaemia cells increases, the body can produce fewer healthy white blood cells, red blood cells and platelets.
Myelodysplastic Syndromes (MDS)
MDS are a very rare group of conditions that occur when the blood-forming cells in the bone marrow become abnormal. The abnormalities include too few functioning red blood cells (which carry oxygen), white blood cells (which fight infection), platelets (which assist blood clotting), or any combination of the three.
MDS is sometimes referred to as a preleukaemic condition because a small percentage of people with MDS develop acute leukaemia as a complication of the disease.