Anemia as a Sign of Colon Cancer

Colon cancer can be a cause of anemia, typically indicated by a lower than normal red blood cell count and hemoglobin level. Anemia though can be caused by many other conditions including other types of cancer. But for colon cancer it may be one of the first signs of a developing malignancy. On the flip side, anemia can be a direct result of radiation and chemotherapy used to treat cancer.

On the whole, anemia is a relatively common condition caused by any number of conditions. There are also different types of anemia which can often give us clues as to what the exact condition is. Such is the case, at least in part, with colon cancer.

Doctor talking to patient in doctor's office
Jon Feingersh / Getty Images

Understanding Anemia

Anemia is simply defined as either the lack of red blood cells that transport oxygen to body tissues or the lack of a protein called hemoglobin that red blood cells need to transport oxygen.

Anemia can often go unnoticed. If symptoms do appear, they are generally minor. In some cases, a person may feel tired or lethargic. Others may have difficulty concentrating or be short of breath when exercising or doing moderately strenuous activity.

In more severe cases, symptoms can include:

  • Pale skin and nail beds
  • Heart palpitations
  • Chest pains (angina)
  • A fast heart rate (tachycardia)
  • Discomfort, numbness, or tiredness of the legs
  • Signs of heart failure

Types of Anemia by Cause

There are three main types of anemia, each of which is differentiated by their cause. They can be broadly defined as follows:

  • Anemia caused by blood loss (trauma, gastrointestinal bleeding)
  • Anemia caused by a breakdown of red blood cells (sickle cell anemia)
  • Anemia caused by decreased red blood cell production (most often attributed to iron deficiency)

It is this latter type that we commonly refer to as iron deficiency anemia.

Anemia as a Sign of Cancer

Iron deficiency anemia can be an early warning sign of cancer and one that is often missed by healthcare providers. In some ways, it’s an understandable oversight given that the condition affects around a billion people worldwide.

Iron deficiency anemia can be caused by everyday life situations such as menstruation, pregnancy, and breastfeeding (which is why iron supplements are often prescribed to women). Children can also be at risk since many begin life with low iron and don't get enough in their diets to meet their daily needs.

Where it is uncommon is in healthy men and postmenopausal women, suggesting a more serious underlying cause. Cancer is one of the things we typically look for, particularly in people over 50 who are at greater risk of the disease.

Research indicates that more than 30% of people with cancer will be anemic at the time of diagnosis with almost half experiencing iron deficiency anemia. The level of anemia rises to about 67% of cancer patients after treatment begins.

How Colon Cancer Causes Anemia

While anemia is closely linked to cancer, the mechanism for its development can vary by the type of malignancy. Some types of cancer, like those affecting the bone marrow, directly impact the body’s ability to produce red blood cells, resulting in severe anemia.

With colon cancer, it works somewhat differently. Bleeding is considered the primary cause of anemia when the colon is involved. This is because the tumor releases certain chemicals that stimulate the formation of new blood vessels. As the tumor grows, the vessel bursts, leading to the loss of red blood cells.

The bleeding, in turn, can give rise to an iron deficiency. Even if there are ample supplies of iron in the blood, the surrounding inflammation can cause iron molecules to become "trapped" in immune cells. As the inflammation persists, the availability of iron becomes less and less, resulting in the development of iron deficiency anemia.

Ensuring the Early Detection of Colon Cancer

If a routine blood test reveals that you are anemic, don’t avoid bringing up the subject of cancer. This is especially true if experiencing symptoms of cancer. In term of colon cancer specifically, the most common symptoms can include:

  • Unintentional weight loss (when not dieting or trying to lose weight)
  • Loss of appetite
  • Nausea or vomiting
  • Changes in your bowel habits
  • Bright red stools or dark red blood in your stools
  • Stools that are thinner than normal("pencil stools")
  • Feeling as if you cannot empty your bowels completely
  • Abdominal discomfort, including bloating, frequent gas pain, or cramps

If any of these symptoms persist for more than two weeks, call your healthcare provider and request the necessary tests to better pinpoint the cause.

4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Väyrynen JP, Tuomisto A, Väyrynen SA, et al. Preoperative anemia in colorectal cancer: relationships with tumor characteristics, systemic inflammation, and survival. Sci Rep. 2018;8(1):1126. doi: 10.1038/s41598-018-19572-y

  2. Wilson MJ, Dekker JWT, Harlaar JJ, Jeekel J, Schipperus M, Zwaginga JJ. The role of preoperative iron deficiency in colorectal cancer patients: prevalence and treatment. Int J Colorectal Dis. 2017;32(11):1617-1624. doi: 10.1038/s41598-018-19572-y

  3. Madeddu C, Gramignano G, Astara G, et al. Pathogenesis and treatment options of cancer related anemia:perspective for a targeted mechanism-based approach. Front Physiol. 2018;9:1294. doi: 10.3389/fphys.2018.01294

  4. Cross AJ, Wooldrage K, Robbins EC, et al. Whole-colon investigation vs. flexible sigmoidoscopy for suspected colorectal cancer based on presenting symptoms and signs: a multicentre cohort study. Br J Cancer. 2019;120(2):154-164. doi: 10.1038/s41416-018-0335-z

Additional Reading

By Suzanne Dixon, MPH, RD
Suzanne Dixon, MPH, MS, RDN, is an award-winning registered dietitian and epidemiologist, as well as an expert in cancer prevention and management.