Anemiacan be an early warning sign ofcolon cancer. It is caused when the tumor starts to bleed, reducing the levels ofred blood cells (RBCs)and an iron-rich protein calledhemoglobinneeded to deliver oxygen and nutrients to tissues.

This can lead to symptoms such as fatigue, weakness, dizziness, and skipped or rapid heartbeats.

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Doctor talking to patient in doctor’s office

This article explains what anemia is, how colon cancer causes anemia, and what signs and symptoms suggest you may have colon cancer. While not always present, especially in the beginning, recognizing any that do occur can help you catch the disease in its early stages when it is most treatable.

Symptoms and Types of Anemia

Anemia can often go unnoticed, though it may be picked up on blood tests done for routine reasons. It is only when the loss of RBCs or iron is severe enough that symptoms may develop and get your attention, most commonly:

Different Types of Anemia

How Colon Cancer Causes Anemia

While anemia with colon cancer is mainly due to blood loss, there are other mechanisms that can complicate the condition.

When amalignant(cancerous) tumor develops, it releases chemicals that trigger the rapid formation of new blood vessels (known asangiogenesis). These new blood vessels provide the tumor with the nutrients it needs to grow but are also very fragile and burst quite easily as the tumor increases in size.

As the tumor gets larger, the bleeding and blood loss worsen. This not only leads to decreased RBCs but a decrease in the amount of iron in the blood, causing iron deficiency anemia.

Studies suggest that more than 30% of people with cancer will experience anemia at some point, with almost half developing iron-deficiency anemia. In those who get chemotherapy or radiation, around 67% can expect to have anemia.

Recognizing the Signs of Colon Cancer

On its own, iron-deficiency anemia is not something one would automatically connect with colon cancer—particularly if it occurs on its own. More likely culprits include heavy menstrual bleeding, an iron-deficient diet, or digestive disorders that impair the absorption of dietary iron (like celiac disedase).

With colon cancer, the healthcare provider will look for other signs of the disease, including:

Severe anemia rarely occurs on its own with colon cancer and it is more commonly seen with some or all of these accompanying symptoms.

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 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.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):1617-24. doi:10.1038/s41598-018-19572-yAmerican Society of Hematology.Anemia.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-yCross 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):154-64. doi: 10.1038/s41416-018-0335-zAdditional ReadingNaoum F.Iron deficiency in cancer patients.Rev Bras Hematol Hemoter. 2016; 38(4): 325–330. doi:10.1016/j.bjhh.2016.05.009

4 Sources

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.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):1617-24. doi:10.1038/s41598-018-19572-yAmerican Society of Hematology.Anemia.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-yCross 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):154-64. doi: 10.1038/s41416-018-0335-zAdditional ReadingNaoum F.Iron deficiency in cancer patients.Rev Bras Hematol Hemoter. 2016; 38(4): 325–330. doi:10.1016/j.bjhh.2016.05.009

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

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):1617-24. doi:10.1038/s41598-018-19572-yAmerican Society of Hematology.Anemia.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-yCross 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):154-64. doi: 10.1038/s41416-018-0335-z

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):1617-24. doi:10.1038/s41598-018-19572-y

American Society of Hematology.Anemia.

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

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):154-64. doi: 10.1038/s41416-018-0335-z

Naoum F.Iron deficiency in cancer patients.Rev Bras Hematol Hemoter. 2016; 38(4): 325–330. doi:10.1016/j.bjhh.2016.05.009

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