The drugs used in chemotherapy are growth inhibitors. They are especially good at turning off cells that are growing very quickly. Unfortunately, the drugs are not selective in their action. They turn off every fast-growing cell. There's no way the drug can tell an abnormal cell from a normal one.
The most important rapidly growing normal cells affected by the drugs are the blood cells . The red cells that carry oxygen are not usually affected very much. But the levels of the white cells that fight infection and the platelets that stop bleeding usually fall during chemotherapy.
There are no signs or symptoms of a minor decrease in blood counts. A slight decrease isn't harmful anyway. In fact, blood counts are expected to fall. This ensures that the drugs are being given in the maximum possible safe dosage. The lowered counts also show your doctor that the drugs are doing what they are supposed to do—stop fast-growing tissues from growing. If there is enough drug in your system to stop white blood cells , then there is enough to have a potential effect on other rapidly growing cells, namely the cancer cells.
Still, it is very important that your doctor keep a close watch on the blood cells. The blood counts have to be measured regularly, usually before each chemotherapy treatment. If the counts are normal, it may be safe to give the standard dose or even increase the drug dosage. If one of the counts is too low, a drug dose can be modified or even put off for a while. When a therapy session is skipped because of low counts, this does not mean that the cancer cells will get out of control. The rest period is a normal part of the therapy, done for safety reasons.
