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Colon cancer—also known as colorectal cancer—can begin with subtle symptoms that are easy to overlook. In many cases, early signs develop gradually and may be mistaken for common digestive issues. As the disease progresses, however, symptoms often become more persistent and noticeable.
(National Cancer Institute; Centers for Disease Control and Prevention)
Being aware of potential warning signs is especially important for adults over age 45 and for individuals with a family history of colorectal cancer. Persistent symptoms should always be evaluated by a healthcare professional.
(Centers for Disease Control and Prevention)
1. What Changes in Bowel Habits May Look Like
One of the earliest and most frequently reported symptoms of colon cancer is a lasting change in bowel habits. These changes often persist for more than a few days and may gradually worsen over time.
Common bowel-related changes include:
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Persistent diarrhea or constipation
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Alternating episodes of diarrhea and constipation
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Stools that appear narrower or thinner than usual
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A sensation that the bowel does not fully empty after a movement
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Increased urgency or frequency of bowel movements
While occasional digestive changes are common and often related to diet, stress, or illness, bowel changes associated with colon cancer tend to persist and do not resolve on their own.
(National Cancer Institute; Mayo Clinic)
Why Colon Cancer Can Affect Bowel Movements
As colon cancer develops, tumors may partially block the intestine or irritate the lining of the colon. This can disrupt how stool moves through the digestive tract, leading to changes in stool shape, consistency, and frequency.
Over time, these disruptions may become more noticeable as tumors grow or inflammation increases within the colon.
(National Cancer Institute; American Cancer Society)
When to See a Doctor
You should speak with a healthcare provider if changes in bowel habits:
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Last longer than two to three weeks
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Occur without an obvious cause, such as diet changes, illness, or new medications
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Are accompanied by additional symptoms, including abdominal pain, unexplained fatigue, rectal bleeding, or unintended weight loss
Early detection of colon cancer significantly improves treatment outcomes. For this reason, persistent bowel changes should never be ignored, particularly in adults over 45 or those with increased risk factors for colorectal cancer.
(Centers for Disease Control and Prevention; National Cancer Institute)
Medical Disclaimer
This content is for informational purposes only and does not substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider regarding symptoms or medical concerns.
Medical citations
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National Cancer Institute (cancer.gov)
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Centers for Disease Control and Prevention (cdc.gov)
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Mayo Clinic (mayoclinic.org)
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American Cancer Society (cancer.org)
2. Blood in Stool
One of the most disconcerting symptoms people report is red blood in their stools, and that’s probably a common cause of alarm for most people. Red blood usually appears when the tumor is located in the descending colon, sigmoid or rectum. That’s because the blood does not have sufficient time to coagulate before showing up in your stools.
However, keep in mind there are many other reasons why you might find red blood in your stools, such as anal fissures, hemorrhoids, diverticulosis, and even harmless colon polyps that may start bleeding without turning into cancer.
3. Abdominal Discomfort or Pain
It is quite common to experience abdominal pain in most gastrointestinal problems, but this makes abdominal pain one of the most unspecific symptoms of colon cancer. It’s usually located in the lower abdomen and often felt as abdominal cramps or colic pain. The pain might be mild or severe, depending on the progression of the disease, and should be coupled with other signs and symptoms to make out the reason why it appears.
4. Unexplained Weight Loss
Finally, one of the most classic symptoms in all types of cancer is unexplained weight loss, and especially in colon cancer. It might be explained by the diarrheic episodes, the anemia, and anorexia, but also because the tumor cells display a very accelerated metabolism that increases the patient’s energy needs.
If there’s no diet or treatment to explain the progressive weight loss, and you’re experiencing the gastrointestinal symptoms we just mentioned, it would be a good idea to run some tests.
5. Fatigue and Weakness
Chronic fatigue is commonly seen in colon cancer, and it might be caused by persistent bleeding and anemia, low nutrient intake, diarrhea, and nutrient absorption problems, and by the cancer cells themselves, which use up a high load of nutrients and energy to keep growing. So, if you ever notice several of these gastrointestinal signs and symptoms along with chronic fatigue, it would be a good idea to pay a visit to your physician to get a full check-up.
- Persistent Fatigue: Experiencing persistent fatigue, weakness, or a sense of lethargy may signal an underlying health concern, including colon cancer.
- Possible Explanation: Fatigue can result from numerous factors, such as inadequate sleep or stress. However, when coupled with other symptoms, it warrants attention.
6. Iron Deficiency Anemia
Anemia
is a condition characterized by a lower-than-normal level of red blood cells or hemoglobin in the blood. It can be associated with colon cancer due to the ways in which the disease can affect the gastrointestinal tract and impact overall blood production. However, anemia itself is a non-specific symptom and can have various underlying causes. If you suspect anemia or any health issue, it’s essential to consult a medical professional for proper evaluation and diagnosis.
In the context of colon cancer, anemia can develop for several reasons:
Chronic Bleeding
One of the common ways colon cancer can lead to anemia is through chronic bleeding. Tumors in the colon can bleed slowly over time, often in amounts that aren’t easily noticeable. This chronic blood loss can result in a gradual reduction in red blood cells and hemoglobin levels, leading to anemia. Blood loss can be seen in the stool, appearing either visibly or through occult blood tests.
Iron Deficiency
Chronic bleeding from colon cancer can also deplete the body’s iron stores. Iron is crucial for the production of hemoglobin, the protein in red blood cells that carries oxygen. When iron levels are low, the body might not produce enough hemoglobin, leading to anemia.
Malabsorption
Advanced colon cancer could potentially affect the absorption of nutrients in the gastrointestinal tract. This might lead to reduced absorption of iron and other nutrients essential for red blood cell production, contributing to anemia.
Symptoms of anemia that might be associated with colon cancer can include:
Fatigue: Due to reduced oxygen-carrying capacity in the blood, individuals with anemia often experience fatigue, weakness, and a lack of energy.
Pale Skin: Anemia can cause a paler complexion, particularly noticeable in the face and mucous membranes.
Shortness of Breath: Reduced oxygen levels in the blood can lead to shortness of breath, especially during physical activity.
Dizziness or Lightheadedness: Anemia can cause a decrease in blood flow to the brain, resulting in feelings of dizziness or lightheadedness.
Cold Hands and Feet: Reduced circulation of oxygen-rich blood might lead to cold sensations in the extremities.
If you experience these symptoms or suspect anemia, especially in combination with other concerning symptoms like changes in bowel habits, unexplained weight loss, or abdominal pain, it’s important to seek medical attention.
A healthcare professional can conduct tests to diagnose the underlying cause of your symptoms and recommend appropriate treatment if necessary.
7. Nausea
Feeling nauseous can be one of the symptoms associated with colon cancer, though it’s important to note that experiencing nausea alone does not definitively indicate colon cancer. Nausea is a non-specific symptom that can occur due to various medical conditions. If you’re concerned about your health, it’s always best to consult a medical professional for a proper evaluation.
That said, in the context of colon cancer, nausea might occur as a result of various factors related to the disease’s progression and effects on the body. Here are some ways in which colon cancer could potentially lead to nausea:
Obstruction:
Colon cancer can cause partial or complete blockages within the colon due to the growth of tumors. These blockages can lead to a backup of intestinal contents, resulting in symptoms such as nausea, vomiting, and abdominal discomfort.
Peritoneal Irritation:
If the cancer has spread and invaded nearby tissues, it might irritate the peritoneum, the lining of the abdominal cavity. This irritation can lead to feelings of nausea.
Chemotherapy:
The feeling of nausea can also be a side effect of chemotherapy, which is a common treatment for colon cancer. Chemotherapy drugs can affect the gastrointestinal system, leading to nausea and vomiting.
Systemic Effects:
As colon cancer advances, it can lead to changes in the body’s overall metabolism and functioning. These changes, combined with the stress cancer places on the body, might result in a general feeling of nausea.
Remember, these are potential reasons for nausea in the context of colon cancer, but they are not exclusive to this disease. Many other conditions can also lead to nausea. If you’re experiencing persistent or severe nausea, especially when accompanied by other symptoms like changes in bowel habits, unexplained weight loss, or blood in the stool, it’s important to seek medical attention to determine the underlying cause and receive appropriate care.
8. Melena
Melena is a symptom characterized by the passage of dark, tarry, and foul-smelling stools. It occurs due to the presence of digested blood in the stool, which indicates bleeding in the upper part of the gastrointestinal tract. While melena can be associated with various gastrointestinal conditions, including ulcers, gastritis, and bleeding from the esophagus or stomach, it can also be linked to colon cancer under certain circumstances.
Colon cancer, particularly when it’s located in the ascending or right side of the colon (where it is closer to the small intestine), might lead to melena. Here’s how:
Advanced Tumor Growth: If a tumor in the colon grows large enough and begins to bleed, the blood can mix with stool as it passes through the colon. The blood undergoes partial digestion in the digestive tract, resulting in the characteristic dark color of melena.
Slow Bleeding: In some cases, colon cancer might cause slow, chronic bleeding that isn’t immediately noticeable. Over time, this ongoing bleeding can lead to the accumulation of blood in the digestive tract, causing melena.
It’s important to note that melena specifically indicates upper gastrointestinal bleeding, which means the bleeding source is likely located in the upper part of the digestive system, such as the stomach or duodenum. However, colon cancer can occasionally cause melena if the tumor is actively bleeding and located in the right side of the colon.
If you notice melena or any other concerning symptoms, such as changes in bowel habits, abdominal pain, unexplained weight loss, or fatigue, it’s crucial to consult a healthcare professional promptly. While melena doesn’t always indicate colon cancer, it’s essential to determine the underlying cause of the bleeding and receive appropriate medical evaluation and treatment.
9. Intestinal gas and bloating
As we mentioned previously, sometimes cancer is large enough to block the regular intestinal transit. That’s why it causes an increase in intestinal gas and bloating. Cancer patients usually experience progressive bloating symptoms, which are aggravated by consuming certain foods. Several diseases might be producing bloating and intestinal gas, such as inflammatory bowel diseases like Crohn’s disease, celiac disease, and many others.
10. Early satiety
It is when you already feel full closely after starting your meal. It might be because you feel nauseous or because you already feel you’re full and don’t need to eat more. Early satiety is not an early sign of colon cancer because it usually appears when the tumor is large enough to affect intestinal transit or cause compression to the stomach, which releases a series of signals interpreted in your brain as if you had a full meal already. However, it is a common symptom not often listed in most guides, and it appears in many patients, causing or contributing to anorexia and weight loss.
