Anemia is an abnormally low level of red blood cells. It occurs when:
The body does not make enough blood.
The body loses blood.
The body destroys red blood cells.
Anemia is common for people with cancer, especially for those receiving chemotherapy. Most people with anemia feel tired or weak. This fatigue can make difficult for patients to cope with the physical and emotional demands of treatment.
Treatment to relieve symptoms and side effects, such as anemia, is an important part of cancer care. This approach is called supportive or palliative care . Talk with your health care team about any symptoms you experience. This should include any new symptoms or a change in symptoms.
About red blood cells
Red blood cells contain hemoglobin. Hemoglobin is an iron protein that carries oxygen to all body parts. When red blood cell levels are too low, body parts do not get enough oxygen. As a result, they cannot work properly.
Red blood cells are made in bone marrow. Bone marrow is the soft, spongy tissue found inside larger bones. A hormone called erythropoietin tells the body when to make more red blood cells. This hormone is made in the kidneys. Therefore, damage to bone marrow or the kidneys can cause anemia.
Signs and symptoms
People with anemia may experience some of these symptoms:
Rapid or irregular heart beat
Occasional chest pain
Dizziness or fainting
Pale skin or lips
Difficulty staying warm
Causes of anemia
Chemotherapy. Chemotherapy  damages bone marrow. Typically, chemotherapy's effect on bone marrow is temporary. And, anemia improves a few months after chemotherapy finishes. Additionally, chemotherapy with platinum drugs may harm the kidneys. These drugs include cisplatin (Platinol) and carboplatin (Paraplatin).
Radiation therapy. Certain types of radiation therapy  damage bone marrow:
Radiation therapy to large areas of the body
Radiation therapy to bones in the pelvis, legs, chest, or abdomen
Certain cancer types. For example, leukemia, lymphoma, and multiple myeloma damage bone marrow. Also, cancers that spread to the bone or bone marrow may crowd out normal red blood cells.
Nausea, vomiting, and loss of appetite. Nausea and vomiting  and lack of appetite  may cause a lack of nutrients. Certain nutrients are needed to make red blood cells. These include iron, vitamin B12, and folic acid.
Excessive bleeding. Sometimes, red blood cells are lost faster than the body is able to replace them. It may happen after surgery or if a tumor causes internal bleeding.
Doctors use a blood test to diagnose anemia. It is called a complete blood count test . The test results include the number of red blood cells. A red blood cell count is measured several ways. The 2 most common measurements are hemoglobin and hematocrit. The hematocrit is the percentage of your blood that is made up of red blood cells.
People with specific cancer types or cancer treatments may have regular blood tests. These look for anemia and other blood-related complications. If test results show that you have anemia, you may need additional tests to find the cause.
Treatment for anemia depends on the cause and symptoms. Here are some examples of how a doctor may treat a patient’s anemia:
Blood transfusion. If anemia causes symptoms, you may need a transfusion of red blood cells.
Medications. If chemotherapy causes anemia, doctors may prescribe erythropoiesis-stimulating agents. These include epoetin alfa (Epogen, Eprex, Procrit) or darbepoetin alfa (Aranesp).
These drugs are forms of erythropoietin grown in the laboratory. They work by telling bone marrow to make more red blood cells.
Epoetin and darbepoetin are given as a series of injections. They can take up to 4 weeks to start working. These drugs are also associated with serious health risks. Learn more about recommendations for epoetin and darbepoetin treatment .
Vitamin or mineral supplements. If a lack of nutrients causes anemia, doctors may prescribe supplements. These include iron, folic acids, or vitamin B12. And, they are usually pills taken by mouth. Occasionally, you may receive a vitamin B12 injection. This may help the stomach absorb the vitamin.
Also, consider eating foods high in iron or folic acid.
Examples of foods high in iron:
- Red meat
- Beans (legumes)
- Dried apricots
- Enriched breads and cereal
Examples of food high in folic acid:
- Lima beans
- Enriched breads and cereals
Side Effects 
National Cancer Institute: Anemia