Chemotherapy and some of other cancer treatments can have negative effects on the production of blood cells. These cells have several functions including defense against disease and carrying oxygen to all of the other cells in our bodies. When cancer treatment reduces the ability of our bodies to generate these cells, fatigue and susceptibility to disease may ensue.
The billions of blood cells that move through our circulatory system (veins, arteries, capillaries) originate from precursors that are located within our bones. These precursor cells have the ability to divide continuously. Since the majority of the cells in circulation have only short lives, the precursor (or stem) cells are able to replace those that die and are eliminated from the body.
The animation below depicts the formation of several different blood cell types from a precursor stem cell. The cells depicted (clockwise from top) include two kinds of polymorphonuclear cells (these include neutrophils), T and B lymphocytes, a megakaryocyte (makes platelets) and a red blood cell (RBC).
Many cancer treatments work by preventing the division of cells. Unfortunately, they often affect normal cells as well as cancer cells. The rapidly dividing cells within the bone marrow are often unintended targets of these drugs. The reduction in the activity of the stem cells in the bone marrow leads to two common side effects seen in cancer patients:
Anemia: a reduction in the number of RBCs in the blood.
Neutropenia: a reduction in the number of neutrophils in the blood.
Many of the blood cells affected by chemotherapy are involved in the protection of the body from disease. The drugs may weaken these defenses. Learn about the immune system.