How Does Colon Cancer Cause Anemia?

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The role of the colon cancer itself in causing anemia


Typically, colon cancer grows slowly (see more in here). The cancer can be present for years before you notice the symptoms. Therefore, there is usually no symptom from the cancer when it is still at early stage.

The size of right colon is relative larger than the left colon. Cancer that grows either in right or left side of the colon can be harmful and even life-threatening if left untreated.

If the cancer grows in the right colon, it can grow and develop to large sizes before it causes the symptoms. This can lead to slow, constant loss of blood, causing anemia.

If it occurs in the left colon, it tends to cause an emergency problem called bowel obstruction. The obstruction can be partial or total (complete obstruction, so thus the waste products cannot pass at all through colon).


In essence, cancer in the digestive system can lead to internal bleeding. The blood usually can be noticed in /on the stool.

However, blood found in the stool doesn’t always point to digestive system cancer. Even many times this symptom is caused by mild condition called haemorrhoids, inflammation in the lower part of the rectum and anus.

The side effects of some cancer treatments

Each treatment for colon cancer should outweigh the risk of potential side effects.

Both radiation therapy and chemotherapy are common treatments for cancer. However, these treatments can pose the risk of anemia, too.

  1. Radiation therapy. The larger area for radiation you take to treat your cancer, the greater risk to have anemia – particularly true if the radiation heats the bones that host lots of bone marrows (the place where red blood cells are produced) such as torso, pelvis, and legs.
  2. Some chemotherapy drugs have potential side effect to cause bone marrow damage.

Other possible contributing factors

These may include:

  1. Poor diet, especially lack of dietary certain vitamins and minerals.
  2. If you also have a major organ problem that links to the production and control of blood cells and oxygen supply in the body, such as severe problems of heart, kidney, liver, or lungs.
  3. Having other conditions that can lead to anemia such as chronic kidney disease and sickle cell disease (inherited anemia). These may cause a low hemoglobin count before you had the colon cancer.

Since anemia can be a serious condition, talk to your doctor if your anemia symptoms persist or last longer than you expect.


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