The short answer
Anemia means your red blood cell count is below normal, so less oxygen reaches your body. Cancer treatment and cancers affecting the bone marrow can cause it. Blood tests confirm it, and treatment depends on your symptoms and the cause.
Anemia is a condition in which the number of red blood cells is below normal.
Chemotherapy, radiation therapy, and cancers that affect the bone marrow can all cause anemia.
A red blood cell transfusion is given when the red blood cell count is low and signs or symptoms of anemia, such as shortness of breath or feeling very tired, occur.
Tell your health care team if you feel very weak and tired, especially if you cannot do your normal activities or are still very tired after resting or sleeping.
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The full explanation.
If treatment has left you exhausted in a way sleep does not fix, anemia is worth checking. It is measurable with a blood test, and there are things your team can do about it.
What anemia is
Anemia is a condition in which the number of red blood cells is below normal. Red blood cells are the cells that carry oxygen from the lungs throughout your body to help it work properly. When you are anemic, your body does not have enough red blood cells, so less oxygen reaches the places that need it.
Why it happens during cancer treatment
Cancer treatments, such as chemotherapy and radiation therapy, as well as cancers that affect the bone marrow, can cause anemia.
Anemia also feeds into the larger problem of cancer-related fatigue. NCI lists anemia among the treatment side effects that can cause or worsen fatigue, along with appetite loss, diarrhea, hot flashes, infection, pain, sleep problems, and vomiting. Chemotherapy destroys healthy cells while treating cancer cells, which on its own can leave you feeling fatigued.
What it feels like
Anemia can make you feel very tired, short of breath, and lightheaded. Signs of anemia may also include feeling dizzy or faint, headaches, a fast heartbeat, and pale skin. Weakness and unusually pale skin are also described as symptoms of anemia.
How it is checked
You will have blood tests to check for anemia. Treatment for anemia is also based on your symptoms and on what is causing the anemia.
So two things drive the plan: the number on your blood count, and how you feel and function day to day. Both belong in the conversation.
When a transfusion is considered, and what it involves
A red blood cell transfusion is given when the red blood cell count is low and signs or symptoms of anemia, such as shortness of breath or feeling very tired, occur. A transfusion is a way of giving you red blood cells to replace blood cells that have been destroyed by disease or by cancer treatment.
A transfusion is not the only option. It is worth asking your team directly: would medicine, iron pills, a blood transfusion, or other treatments help me? The right answer depends on the cause and on your symptoms.
There is one longer-term consideration if transfusions become routine. Patients who receive many blood cell transfusions may have tissue and organ damage caused by the buildup of extra iron. These patients may be treated with iron chelation therapy to remove the extra iron from the blood. If you are heading toward repeat transfusions, ask how your iron levels will be watched.
Ways to manage anemia
These are the steps NCI suggests if you have fatigue caused by anemia.
- Save your energy and ask for help. Choose the most important things to do each day. When people offer to help, let them do so. They can take you to the doctor, make meals, or do other things you are too tired to do.
- Balance rest with activity. Take short naps during the day, but keep in mind that too much bed rest can make you feel weak. You may feel better if you take short walks or exercise a little every day.
- Eat and drink well. Talk with your doctor, nurse, or a registered dietitian to learn what foods and drinks are best for you. You may need to eat foods that are high in protein or iron.
When to tell your health care team
Tell your health care team if you feel very weak and tired, especially if you are not able to do your normal activities or are still very tired even after resting or sleeping.
Also report new or worsening signs of anemia: shortness of breath, feeling lightheaded, dizzy, or faint, headaches, a fast heartbeat, or pale skin.
Because thresholds differ from person to person and treatment to treatment, ask your own team the question NCI recommends asking: what problems should I call you about? Get that answer before you need it, and write down the number you should use.
Questions to ask your health care team about anemia
- What is causing the anemia?
- What problems should I call you about?
- What steps can I take to feel better?
- Would medicine, iron pills, a blood transfusion, or other treatments help me?
- Would you give me the name of a registered dietitian who could also give me advice?
Sources
- National Cancer Institute — Anemia: Cancer Treatment Side Effect: https://www.cancer.gov/about-cancer/treatment/side-effects/anemia
- National Cancer Institute — Fatigue and Cancer Treatment: https://www.cancer.gov/about-cancer/treatment/side-effects/fatigue
- National Cancer Institute — Myelodysplastic Syndromes Treatment (PDQ), Patient Version: https://www.cancer.gov/types/myeloproliferative/patient/myelodysplastic-treatment-pdq
Words to know
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Common questions
Why does cancer treatment cause anemia?
Cancer treatments such as chemotherapy and radiation therapy, as well as cancers that affect the bone marrow, can cause anemia. When you are anemic, your body does not have enough red blood cells to carry oxygen from your lungs throughout your body.
When would I need a blood transfusion?
A red blood cell transfusion is given when the red blood cell count is low and signs or symptoms of anemia, such as shortness of breath or feeling very tired, occur. Ask your team whether medicine, iron pills, a blood transfusion, or other treatments would help you.
Are there downsides to having many transfusions?
Patients who receive many blood cell transfusions may have tissue and organ damage caused by the buildup of extra iron. These patients may be treated with iron chelation therapy to remove the extra iron from the blood.
Questions to ask your doctor
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Written by: Cancer Explained Editorial TeamSources last checked: 2026-07-28Last updated: 2026-07-28Next planned review: 2027-07-28
How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status — Source verified. This page was created with AI assistance and checked against the sources listed on it. Source checking is not a medical review.
General education — varies by person. Answers genuinely differ between people. This page explains what commonly varies and points you to your care team for your situation.
Human medical review: not completed. Cancer Explained is not clinician-reviewed, and that is a deliberate design choice rather than a gap we are waiting to close. We restate published federal guidance and cite it; the authority belongs to the source, not to us. That is why every page names where its claims come from — so you can verify us instead of trusting us. Use it to understand your situation and to ask better questions of the people treating you.
How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source verified — This page was created with AI assistance and checked against the sources listed on it. Source checking is not a medical review.
Human medical review: not completed. Cancer Explained is not clinician-reviewed, and that is a deliberate design choice rather than a gap we are waiting to close. We restate published federal guidance and cite it; the authority belongs to the source, not to us. That is why every page names where its claims come from — so you can verify us instead of trusting us. Use it to understand your situation and to ask better questions of the people treating you.
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