What causes anemia during cancer treatment?

Two main routes: the treatment itself, and the cancer. Chemotherapy and radiation therapy can cause anemia, and so can cancers that affect the bone marrow.

Anemia means the number of red blood cells is below normal. Red blood cells carry oxygen from your lungs to the rest of your body, so when they run short, everything that needs oxygen works harder.

Why treatment does this

Bone marrow is the soft tissue in the center of bones where blood cells are made. Chemotherapy targets fast-dividing cells. The cells that produce blood divide constantly, so they take collateral damage. Radiation aimed at areas with a lot of marrow does the same thing locally.

Cancers that start in the marrow, or spread to it, crowd out that production directly. Leukemia, lymphoma, myeloma, and myelodysplasia all appear on the MedlinePlus list of marrow problems that cause anemia.

Timing follows the cycle. Healthy red blood cells last about 90 to 120 days, far longer than white blood cells. So anemia from chemo usually builds over weeks. It does not show up after one dose.

The causes that have nothing to do with cancer

This is the part worth pushing on, because more than one cause can be running at once and each has a different fix.

Iron deficiency is the most common form of anemia in general. Slow blood loss often drives it, whether from stomach ulcers, a bleeding tumor, or heavy periods. Vitamin B12 and folate deficiency both cut red blood cell production. Surgery that removes part of the stomach or intestine can block absorption of those nutrients. Certain medicines cause anemia. So does long-term kidney disease. The kidneys make erythropoietin, the hormone that tells marrow to produce more red cells.

NCI's guidance points the same way. Treatment for anemia is based on your symptoms and on what is causing it. That is why "would iron pills help me" has no single answer. Iron helps iron deficiency. It does nothing for B12 deficiency.

What it feels like, and when to call

Early on you may notice nothing, especially if it develops slowly. First symptoms are usually feeling weak or tired more than usual. Others are headaches, trouble concentrating, irritability, loss of appetite, and numbness or tingling in the hands and feet.

As it worsens, NCI lists shortness of breath, lightheadedness, dizziness or feeling faint, a fast heartbeat, and pale skin.

Call 911 or go to an emergency department for chest pain, or for shortness of breath while you are sitting still. Call your team the same day if you faint, or if your heart rate stays fast while you sit still. Those go beyond fatigue. Also report black or tarry stools, or blood in your stool or vomit. That points to bleeding rather than marrow damage. It is treated differently, and fast.

Blood tests are how anemia is actually found and tracked, so the number in your chart usually moves before you feel much.

Managing it day to day

NCI's practical advice for anemia-related fatigue is short. Save your energy and let people help with driving and meals. Balance rest with activity. Too much bed rest causes weakness, while short walks often help. Eat and drink well, and ask for a referral to a registered dietitian. You may need more protein or iron.

Ask your team four things. What is causing your anemia. Which problems to call about. Whether medicine, iron, or a transfusion would help. And what your hemoglobin trend looks like across cycles. Our guide to anemia covers treatment options, and the piece on fatigue covers the exhaustion that usually comes with it.

Sources

• https://www.cancer.gov/about-cancer/treatment/side-effects/anemia
• https://medlineplus.gov/ency/article/000560.htm