Leukemia refers to several cancers that affect the blood-forming system ("blood cancer"). All forms have out-of-control and rapidly multiplying leukocytes (white blood cells). Depending on the course, a distinction is made between acute and chronic leukaemia.
Chronic leukaemias are often diagnosed late because they develop slowly and often without symptoms. The out-of-control blood cells are relatively mature, in contrast to the acute variant, which is caused by immature leukocytes. Chronic leukemias almost invariably affect adults.
The umbrella term chronic leukemia can be further divided into two main groups:
Chronic Lymphocytic Leukemia (CLL).
In CLL, the lymphocytes (a subspecies of white blood cells) are out of control. Their function in a healthy person is immune defence. Acute lymphatic leukaemia (ALL) also originates from the lymphocytes, but the degeneration occurs at an earlier stage of the cells' development.
Chronic lymphatic leukaemia is the most common form of all leukaemias. Every year, 3 out of every 100,000 people contract it. The average age of those affected is 65.
CLL is nowadays often counted among the lymphomas (malignant changes in the lymphatic system) because the lymph nodes are also attacked.
Chronic myeloid leukaemia (CML)
The basis for CML is the development of cancer cells from blood stem cells. The disease is divided into 3 stages: "Chronic Stage" develops slowly and if left untreated, progresses to the "Acceleration Stage" which progresses faster and is more dangerous. Finally, the "blast crisis" occurs, which resembles acute leukemia.
Chronic myeloid leukaemia is comparatively rare. It affects only 1 person out of 100,000 annually. Most of the patients are middle-aged.