Symptoms of Colon Cancer

As the third leading cause of cancer-related deaths in the United States, it's important to know the symptoms of colon cancer so you can do your best to catch it early, when it's most treatable. Some include cramping belly pain, dark or bright red blood in your stool, or a change in your stool frequency, like persistent diarrhea or constipation. Whole-body symptoms like unintentional weight loss, loss of appetite, or unusual tiredness may also occur in colon cancer. Iron deficiency anemia and jaundice, which are complications of colon cancer, may also develop.

Research has shown that there is a significant delay between when people notice signs of colon cancer and when it is actually diagnosed. This lag time, which averages around five months, could result in a colon cancer spreading further and lowering the chance of a cure. While it's true that most people with these symptoms do not have colon cancer, it's never safe to assume that's the case.

colon cancer symptoms
Illustration by Verywell

Anatomy

In order to understand what colon cancer symptoms might feel like, it helps to briefly review the anatomy of the colon.

The colon makes up most of the large intestine, which is approximately six feet in length, the last six inches or so of which are comprised of the rectum and anal canal. Many people think of the small intestine as being "on top" and the large intestine as being down below, but there is actually overlap, and much of the large intestine lies above the small intestine.

The colon is shaped like a lean-to, with the ascending colon traveling up the right side of your abdomen, the transverse colon traveling horizontally across your upper abdomen, and the descending colon traveling from just under your ribs on the left, down to the rectum and anus.

Frequent Symptoms 

In the early stages of colon cancer, people often have no symptoms. This is why regular screening beginning at 45 (and earlier for those with risk factors) is an important investment in your health.

It's key to note, as well, that the symptoms mentioned below are by no means a "slam dunk" clue of a colon cancer diagnosis. In fact, they could indicate another problem in the bowels like an infection (for example, acute diverticulitis), hemorrhoids, or inflammation (for example, Crohn's disease). This is why being evaluated by your doctor is critical. 

Colon cancer symptoms come in two general varieties, local symptoms (based on where in the colon the tumor is located) and systemic or whole-body symptoms.

Local

Local colon cancer symptoms affect your bathroom habits and the colon itself. Some of the common local symptoms of colon cancer include:

Changes in Your Bowel Habits

There is no such thing as a universally "normal" bowel movement. In fact, your doctor really only cares about what is normal for you. In other words, everyone’s stool size, color, and consistency are unique. In the end, different people have different bowels habits.

The important thing to be alert for is any change in your normal pattern of bowel movements.

The nature of a bowel movement change can be described in the following ways:

  • Change in stool frequency: A persistent change (more than a few days) in stool frequency is one potential sign of colon cancer. So, for example, if it is normal for a person to have three bowel movements per day, and he or she is having only one per day, or one every other day, this may signal constipation. On the other hand, another person's typical bowel pattern may be to have a bowel movement every other day. In this case, having one bowel movement per day may be unusually frequent, and it may signal a change in typical bowel habits.
  • Change in stool shape: Thin or narrow stools, often described as ribbon- or pencil-like, may also be a sign of colon cancer. In an otherwise healthy person, thin stools may be caused by a narrowing of the colon, also called a partial blockage of the colon due to colon cancer. Think of your colon as a hollow tube, like a drinking straw: If a tumor is growing inside the colon, it can start to obstruct the flow of stool through it, just like a pea inside a drinking straw would block or slow the flow of fluids.
  • Changes in stool color: Bleeding in the colon due to colon cancer may result in bright red or dark red blood in the stools. More specifically, if bleeding is in the ascending (right-side) colon, the stools may be more maroon or purple in color since the bleeding is occurring farther away from the rectum. If the tumor is in the descending (left-side) colon, the bleeding tends to result in bright red stools (the passage of fresh, red blood is called hematochezia).
  • Difficulty with stool evacuation: A persistent feeling that you need to have a bowel movement, even when you just had one (called tenesmus), may be a symptom of colon cancer. 

Intermittent (Alternating) Constipation and Diarrhea

It's not uncommon for colon cancer to result in symptoms of alternating diarrhea and constipation. This may occur when there is a partial obstruction in the bowel due to a tumor. Constipation may occur due to difficulty in stool passing the obstruction, followed by diarrhea when backed up contents are then passed.

Abdominal Discomfort

Abdominal pain or cramping may occur for several reasons in those who have colon cancer. Most frequently, abdominal pains or cramps are associated with cancers on the left side of your colon. Cramps may also be associated with advanced colon cancer: As the tumor grows through the colon or bleeds, it may irritate the lining of the abdomen.

Gas and Bloating

While it's normal to pass gas up to 23 times per day, excessive gas and bloating can be a sign of colon cancer. However, dietary triggers (for example, carbonated beverages, dairy products, and high-fiber foods) and digestive disorders (for example, inflammatory bowel disease) are more common culprits.

If gas and bloating are due to colon cancer, they tend to be late symptoms caused by an obstructing tumor in the colon. Bloating may also occur as a result of cancer spreading to nearby lymph nodes. 

Nausea and/or Vomiting

When nausea and vomiting are symptoms of colon cancer, it's usually because a tumor is causing a bowel obstruction, usually in the proximal colon (meaning the end closer to the small intestines). Nausea and vomiting may occur at any stage of colon cancer but are more common with advanced disease. 

It's important to remember that the occurrence of nausea and vomiting alone, without other colon cancer symptoms, is unlikely an indication of cancer. There are lots of reasons for feeling sick and throwing up. That being said, if nausea and vomiting are accompanied by other worrisome signs such as constipation, abdominal cramping, and/or abdominal distension, colon cancer could be a cause. 

Systemic

Systemic colon cancer symptoms are those that affect your whole body and include:

Unintentional Weight Loss

If you lose weight without trying, you may, at first, be pleased. But unintentional weight loss is an important symptom that shouldn't be ignored. Colon cancer is only one of several serious conditions that might first declare themselves with unexpected weight loss.

Unintentional weight loss is described as losing 5 percent or more of body weight over a six- to 12-month period. For example, if a 150-pound woman lost 7.5 pounds in a year for no apparent reason, she should contact her physician.

The basis behind unintentional weight loss with cancer is that tumors use your body's blood and nutrients to thrive and grow. In addition, some tumors release chemicals that increase the body's metabolism, which can further lead to unexplained weight loss. 

Loss of Appetite

The idea of a tumor as its own life form may also partially explain why many people with cancer do not want to eat; unusual loss of appetite is another sign to look out for. While the loss of appetite most often occurs with advanced cancers, it has been noted in some people with early colon cancer.

Unexplained Fatigue

Extreme tiredness is a nonspecific symptom but is very common in people with more advanced cancers. Cancer fatigue differs from "ordinary" fatigue in that it's not usually relieved by rest and isn't counteracted by a good cup of coffee.

Feeling "Off"

It's not uncommon for people to have a sense that something is amiss in their body, even if they don't have specific symptoms to back up that feeling. Trust your intuition. If you are concerned that something is wrong, it could be. Make an appointment and talk with your doctor.

Rare Symptoms

If colon cancer is not diagnosed until its advanced stages, it may cause one or more of these symptoms: 

Fever

If a tumor in the colon breaks through the intestines, an abscess, which causes a fever, may occur.

Air Bubbles in Urine

Air bubbles in your urine (called pneumaturia) may occur if a tumor in the colon invades into the bladder.

Problems Breathing

If the colon cancer has spread to the lungs, shortness of breath, coughing, and/or chest pain may occur. 

Headache and Neurological Problems

If the colon cancer spreads to the brain or spinal cord, a headache, vision changes, confusion, and/or seizures may occur.

Bone pain 

Fractures, bone pain, and high calcium levels (seen on a blood test) may occur if cancer spreads to the bones.

Complications

There are a few complications that may arise as a result of colon cancer.

Iron Deficiency Anemia

Due to microscopic bleeding from a tumor, iron deficiency anemia may occur as the first sign of colon cancer. Anemia is diagnosed with a blood test, called a complete blood count (CBC), and may cause symptoms of unusual tiredness, dizziness, palpitations, and shortness of breath.

Bowel Obstruction

A bowel obstruction from colon cancer means that the tumor is physically blocking the intestines. Depending on the severity of the blockage, solids, liquids, and even gas may be prevented from passing through the colon. This can lead to painful stomach cramps, bloating, and constipation, and sometimes nausea and/or vomiting.

While a nasogastric tube may be placed temporarily to reduce swelling and remove the fluid and gas buildup of a bowel obstruction, surgery to remove the obstructing tumor or a stent placement (to open up the blocked area) is often required. 

Jaundice

Another potential complication of colon cancer is jaundice, a condition in which the skin and whites of the eyes take on a yellowish appearance. Jaundice may occur when colon cancer spreads to the liver, a common site of metastasis. It may also occur due to pressure from a colon cancer on important structures related to the liver. 

When to See a Doctor

While many people have heard that having blood in their stools may be a sign of colon cancer, just about any change in your bowel habits is worth evaluating. While you may be anxious about the possibility of having colon cancer, early diagnosis offers you the best opportunity for treatment success. In addition, there is a possibility that something entirely else is going on—something less serious than cancer.

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