Cancer and its treatment can cause a drop in red blood cells (anaemia). Here we explain why and what can be done to help.


What is anaemia?

Anaemia means you have a lower than normal level of red blood cells circulating in your bloodstream. Because red blood cells carry oxygen from the lungs to all the cells in the body, anaemia can cause tiredness and breathlessness. You may also feel low or depressed when you’re anaemic.

What causes anaemia?

Like white blood cells and platelets, red blood cells are made in your bone marrow. Their natural lifespan in the bloodstream is much longer than for white blood cells, at around 120 days. Then they naturally die off. There are two types of bone marrow. Blood cells are made in the red bone marrow, which is in your pelvis, ribs, backbone, breastbone, skull and shoulder blades.

If your body needs more replacement red blood cells than your red bone marrow is making, you will have a shortfall and be anaemic. Because red blood cells live longer than white cells, anaemia takes longer to show up than a drop in white cells.

There are many situations that can lead to anaemia. Some are related to the body being unable to make enough red cells to keep up with demand. Or you may be losing more red blood cells than you’re making. Those relevant to having cancer include:

  • The cancer itself
  • Cancer treatments – radiotherapy and chemotherapy
  • Losing blood – after surgery or from a cancer, such as a stomach or bowel cancer for example
  • Missing vitamins or minerals in the diet because of not eating enough

Why cancers cause anaemia

We know that specific cancers such as leukaemias, lymphomas and myelomas can affect the bone marrow and blood counts. In these blood cancers, the cells grow in the bone marrow and start to take over, leaving less room for blood cell production. 

But overall, around 1 in 3 people diagnosed with cancer are already anaemic. Like all cells, cancers produce proteins that they use to signal to each other. Some of these signalling proteins affect how red blood cells are produced, how long they live in the blood and how the body uses iron and oxygen. Together, these effects often lead to anaemia.

Some cancers also cause bleeding. For example, that’s the basis of bowel cancer screening – looking for blood from a tumour that’s bleeding in the bowel. 

Why cancer treatments cause anaemia

Chemotherapy and radiotherapy work because they kill cells that are multiplying – such as cancer cells. Other healthy body cells that multiply frequently will also be killed off by treatment. The cells of the red bone marrow multiply all the time, making new blood cells as those in the circulation are used up (in the case of white cells fighting infection) or die off at the end of their natural lifespan.

You notice the effects of treatment on your white cells much sooner because they don’t live so long. Because red cells live for around 3 months, it takes a while for the level in the blood to drop. 

Chemotherapy circulates throughout your body so it reaches all your bone marrow and kills off developing blood cells, causing your counts to drop. 

Radiotherapy only affects the area of the body it’s aimed at. So it won’t cause a drop in blood cells unless a significant amount of red bone marrow is inside the treatment area. If you need total body irradiation for a bone marrow or stem cell transplant, pretty much all of your bone marrow will be affected and you will develop low blood cell counts. You may also develop anaemia if you have radiotherapy to the long bones of your legs, your pelvis or your chest as these areas contain the bones that are most involved in blood cell production.

For some cancers, you have combined chemotherapy and radiotherapy so are even more likely to become anaemic in time.

What can be done to help?

The immediate treatment for anaemia is a blood transfusion. You may have what doctors call ‘packed cells’, which is blood with some of the plasma taken out. So it has a high concentration of red blood cells. If you’re tired and breathless, it’s the quickest route to feeling better.

Your body needs iron to make red blood cells, so your doctor may ask you to take iron tablets if you are anaemic. If you are only mildly anaemic, this may be enough treatment, but with cancer you will often need a transfusion for a quick top up of red blood cells.

Doctors also use medicines to try and prevent anaemia or get rid of it more quickly. EPO (or erythropoietin) is a natural body chemical normally made by your kidneys which we can now make in the lab. It encourages your bone marrow to make red blood cells. You are more likely to have this if you have anaemia after high dose chemotherapy, platinum chemo for ovarian cancer or myeloma that has affected your kidneys.

There isn’t a great deal you can do yourself to help with anaemia. Pace yourself if you’re tired and breathless. Your body can only provide so much oxygen until your red cell count recovers so there’s no sense in overdoing it. If you aren’t eating well, taking an iron supplement may help to prevent anaemia and give you the iron your body needs to make red blood cells. Foods that contain iron include:

  • Liver 
  • Meat
  • Beans
  • Nuts
  • Dried apricots
  • Brown rice and other whole grains
  • Fortified breakfast cereals
  • Soybean flour
  • Dark-green leafy vegetables

Do tell your doctor straight away if you are feeling tired and breathless. If you are anaemic, the sooner you are treated for it, the sooner it’ll be under control and you’ll feel better.


Related article: Why does cancer treatment increase your risk of bruising and bleeding? (Plus tips on how to manage