With chronic leukemia, “leuk” refers to white blood cells, and “emia” refers to the blood; so in chronic leukemia there are lots of partially developed white blood cells in the blood over a long period of time.
These partially developed white blood cells interfere with the development and function of healthy white blood cells, platelets, and red blood cells.
Now, every blood cell starts its life in the bone marrow as a hematopoietic stem cell.
Hematopoietic stem cells are multipotent -- meaning that they can give rise to both myeloid or lymphoid blood cells.
If a hematopoietic stem cell develops into a myeloid cell, it’ll mature into an erythrocyte -- or a red blood cell, a thrombocyte -- or a platelet, or a leukocyte -- or a white blood cell, like a monocyte or granulocyte.
Granulocytes are cells with tiny granules inside of them -- they include neutrophils, basophils, and eosinophils.
If a hematopoietic stem cell develops into a lymphoid cell, on the other hand, it’ll mature into some other kind of leukocyte: a T cell, a B cell, or a natural killer cell, which are referred to as lymphocytes.
Once the various blood cells form, they leave the bone marrow, and travel around the blood, or settle down in tissues and organs like the lymph nodes and spleen.
Chromosomal abnormality in hematopoietic stem cells that are destined to become leukocytes is the most common cause of chronic leukemia.
Some examples of abnormalities include a chromosomal deletion, where part of a chromosome is missing, a trisomy, where there’s one extra chromosome, and a translocation, where two chromosomes break and swap parts with one another.
Now there are two types of chronic leukemia.
The first is chronic myeloid leukemia, CML, which is caused by a particular chromosomal translocation that affects granulocytes.
The second is chronic lymphocytic leukemia, CLL, which is caused by a variety of chromosomal mutations that affect lymphocytes, in particular B cells.