Leukemia

Leukemia is a cancer of the blood-forming tissues, that disrupts the normal function of bone marrow. This disruption leads to the proliferation of immature white blood cells.

Leukemias are classified as acute or chronic, and by the type of cells affected, either myeloid or lymphoid. The four primary types of leukemia include acute lymphoid leukemia, or ALL; chronic lymphoid leukemia, or CLL; acute myeloid leukemia, or AML; and chronic myeloid leukemia, or CML.

Now, bone marrow is a spongy tissue found in the center of most bones. It contains stem cells, which are unspecialized cells that, through a process called hematopoiesis, differentiate into functional cells such as red blood cells, or RBCs; white blood cells, or WBCs, also called leukocytes; and platelets. Hematopoiesis is a continuous process that ensures there’s a steady supply of cells to replace old and damaged cells.

As far as WBCs go, there are several types which come from two distinct stem cell lines: the lymphoid line, and the myeloid line. Immature cells, called blast cells, are formed from these stem cell lines and further differentiate into functional WBCs. In the lymphoid line, lymphoblasts produce lymphocytes, including B-cells, T-cells, and natural killer cells. In the myeloid line, myeloblasts produce neutrophils, eosinophils, basophils; and monoblasts produce monocytes. These cells function as part of the immune system, fighting infection and other diseases, and removing foreign substances from the body.

While the exact cause of leukemia is not fully understood, genetic and environmental factors play a role. Inherited genetic conditions associated with an increased risk of leukemia include Down syndrome and neurofibromatosis. Other genetic changes such as chromosomal translocations, where pieces of two chromosomes split off and swap places, like with the Philadelphia chromosome, are also associated with an increased risk of leukemia.

Environmental factors include exposure to ionizing radiation, cigarette smoke, and certain chemicals like benzene. In addition, epigenetic modifications like DNA methylation can also increase the risk of leukemia. Lastly, ALL is more common in children, while CLL is more common in adults over the age of 65.