Colon Cancer Symptoms You Need to Know

Cancer is responsible for millions of death around the world every year. By some estimates, colorectal cancer is the second-leading cause of cancer-related death (for men and women combined) in the United States every year.

Colon Cancer can disrupt healthy colon function.

However, in some people, this efficient process can become disrupted when the cells of the rectum or the colon become abnormal and grow uncontrollably. This process typically begins with small masses of cells called polyps. Fortunately, in many cases, the polyps are benign (non-cancerous).

Unfortunately, there are times when these polyps are malignant (cancerous). In these cases, a person has colon cancer or colorectal cancer.

What are the symptoms of colon cancer?

While most people over the age of 50 are encouraged to get regular colonoscopies, it’s important to remember that cancer can strike at any age and in between appointments. Since catching cancer early is the best way to handle this disease—no matter the type—that makes spotting the early warning signs crucial for improving odds of colon cancer survival.

So, just what symptoms point to colon cancer? As most would probably guess, many of the warning signs affect gastrointestinal functions…

Changes in Stool Appearance

Can stool gives clues about overall health?

Yes. The size, color and shape of stool can give someone an indication of their overall health.

For example, small, hard stools likely indicate constipation. Conversely, if stools suddenly become narrow and thin like a pencil, it could indicate that something is obstructing the bowel, such as cancerous tumors.

What will the stool look like?

Changes to stool that warrant medical attention include:

  • Pencil-thin stool coupled with bleeding and unintended weight loss
  • Black stool, which can also indicate bleeding
  • Bright red stool, which can indicate a tumor on the left side of the colon
  • Purple or reddish-purple stool, which can indicate bleeding on the right side of the colon

Cancer or something else?

There are many diseases and conditions that can cause bloody stool, such as Crohn’s disease, irritable bowel syndrome, and ulcerative colitis. So, while bloody stool alone does not always indicate cancer, it does mean a trip to the doctor is warranted, as these conditions are all serious.

Other changes in stool color or shape may happen because of something as simple as dietary changes. However, stool that is pencil thin or that changes in shape and lasts for more than a few days is cause for alarm. This fact is especially true when paired with the following symptom…

Gas and Bloating

What is bloating?

Bloating simply refers to when a person’s abdomen swells. In many cases, the abdomen will feel full; sometimes bloating is so severe that clothes look and feel tighter. It’s common for passing gas to accompany bloating.

Now, it’s normal to pass gas many times each day. However, passing an excessive amount of gas along with other symptoms like bloating can be a sign of trouble.

Why does cancer cause bloating and gas?

Passing a lot of gas is often a late-stage sign of colorectal cancer. The bloating that often accompanies gas is usually caused by the cancer spreading to the lymph nodes.

Cancer or something else?

Passing gas is a normal bodily function, and the occasional bout of excess is often no cause for serious alarm. After all, drinking dairy or carbonated beverages can result in this symptom. Passing a lot of gas could also be a sign of a stomach or intestinal tract issue, especially when paired with the following alarming signs…

Fatigue and Anemia

What is fatigue?

Fatigue is more than feeling a little sleepy. It is an intense feeling of exhaustion and tiredness that persists even after adequate amounts of sleep. Struggling to complete daily activities and feeling tired despite a lack of physical movement are both signs of fatigue.

What is anemia?

Anemia is a condition where there is a reduced amount of red blood cells that importantly transport oxygen. Now, anemia can cause other symptoms, including:

  • Low energy/fatigue
  • Dizziness/lightheadedness
  • Shortness of breath

How can cancer cause anemia and fatigue?

Colorectal cancer can cause bleeding in the rectum. As previously stated, this blood can appear in the stool. If colorectal bleeding continues, it can also cause anemia, as blood loss and the subsequent loss of iron can lead to this condition.

Cancer or something else?

It is important to remember that anemia is a common condition that can be caused by something as simple as not eating enough iron-rich foods. For these people, adding more iron to their diet through foods or supplements may help.

However, anemia along with the following is cause for concern…


What is constipation?

Constipation is the condition where someone is unable to pass stool, even if they feel like they really need “to go.” However, straining to pass stool or passing hard stools are both signs of constipation, too. Healthy stool, by contrast, should be of medium hardness and pass easily (without straining).

How does constipation happen?

When fecal matter stays in the colon, it hardens, which makes it more difficult to pass. So, why does this hardening occur, anyway? Sometimes it’s simply the result of eating certain foods or not getting enough fiber. Lack of exercise and dehydration can also cause constipation.

How can someone spot this symptom?

Everyone’s bowel movements are different. Some people pass stool several times per day. Others only pass stool a few times per week. It is normal to have a regular pattern, but what counts as “regular” varies by individual. In other words, there is no single criteria for how much stool someone has to pass regularly before they are considered irregular—it all depends on the individual.

Self-knowledge is key.

Namely, the key to knowing if something is wrong is knowing one’s own routine and if there are any disruptions to the routine. Typically, a colon cancer patient might notice changes in their bowel movements. For instance, stool might become harder than usual, and this change might last for longer than a month at a time.

Cancer or something else?

Constipation alone is not always an indication that a person has cancer. However, constipation in conjunction with other symptoms of colon cancer may be a cause for concern. In other words, those who notice constipation as well as some of the following symptoms should speak with a doctor about their concerns.

Now, while colon cancer might cause some people to experience constipation, it can make others develop the opposite problem…

Unexpected Weight Loss

Because the colon is such an essential part of the digestive system, any minor changes in its functioning can lead to a loss of appetite and weight loss. So, weight loss is not always a sign of cancer, although it is common in cancer patients.

How can cancer cause weight loss?

There are many reasons a cancer patient may lose weight, including:

1. Lack of Appetite or Weakness and Nausea

In many cases, weight loss could be due to a lack of appetite. Feeling full after eating only a small amount of food is also common in some cancer patients. Others report feeling too weak or nauseated to eat.

2. Fighting Cancer Requires Lots of Energy

Cancer cells can expend a lot of the body’s energy, which can reduce the patient’s energy and also lead to weight loss. Additionally, the body uses up a lot of energy as the immune system fights cancer, which further contributes to fatigue and weight loss.

3. Cancer-Fighting Drugs and Therapy

After cancer is diagnosed, cancer-fighting drugs and therapies could also cause the patient to feel sick and eat less. Chemotherapy, for example, commonly induces nausea and vomiting.

Cancer or something else?

Losing weight by itself is not necessarily indicative of cancer. However, those who lose 10 or more pounds without trying should see a doctor, especially if they notice the following as well…


What is diarrhea?

Diarrhea is a condition where the stool becomes loose and watery. In addition to changes in stool consistency, diarrhea can also make someone urgently feel like they have “to go” much more frequently than what is normal for them.

How does cancer cause diarrhea?

In patients with colorectal cancer, tumors can prevent the colon from effectively processing waste. This prevention causes waste to be expelled from the body in a more liquid form. In many cases, a cancer patient actually alternates between diarrhea and constipation.

This unpleasant situation all starts when a tumor partially obstructs the patient’s bowel. When this obstruction happens, the patient is constipated and struggles to pass the stool. Following this unpleasant situation, the patient’s bowels become loose, and the backed-up stool is released as diarrhea.

Cancer or something else?

In most cases, diarrhea alone is not an indication of a serious health problem, as it can be caused by conditions like a simple stomach flu. In fact, it is perfectly normal to experience short-term diarrhea a couple of times a year. Fortunately, most forms of diarrhea clear up after a few days.

However, those who experience persistent (lasting) diarrhea along with stomach cramps and blood in the stool should seek medical attention. Even if the cause of the diarrhea is not colon cancer, it is still worth it to get a check-up.

It’s unpleasant, but it pays to look at what is left behind.

Those who notice changes in their bowel movements should also take notice of what exactly they are leaving behind in the toilet, as it could be another sign of cancer…

Nausea and Vomiting

Why does cancer cause nausea?

When nausea and vomiting are present in patients with colon cancer, it’s most often because a tumor has created a bowel obstruction. This obstruction will most often be found in the proximal colon, which is the end closest to the small intestine.

What stage will this symptom be present?

Vomiting and nausea can be present at any stage of cancer. However, these symptoms are more common in the advanced stages.

Cancer or something else?

Nausea and vomiting are symptoms of many illnesses, such as the flu or even the common cold. So, nausea and vomiting alone do not necessarily mean a person has cancer.

However, if nausea and vomiting are present alongside other symptoms, like the following, it could be a cause for concern…

Abdominal Cramps

Cramping and abdominal pain are also symptoms of colon cancer.

How does cancer cause cramping and pain?

This kind of cramping and pain are caused by a tumor growing and/or bleeding, which irritates the abdominal lining. Specifically, pain in the abdomen can indicate cancer along the left side of a person’s colon.

What stage will cramping be present?

Cramping is sometimes associated with an advanced stage of colon cancer.

Cancer or something else?

As with most of the symptoms mentioned here, abdominal cramps alone are not always an indication of cancer. However, cramping and pain are reason enough to see a physician for treatment, especially if you have other symptoms, such as the following…


What is jaundice?

Jaundice is a condition in which a person’s skin and the whites of the eyes turn yellow. Jaundice itself is usually a symptom of an underlying disease or problem.

How can cancer cause jaundice?

While jaundice is not a common symptom of colon cancer, jaundice does sometimes appear in patients after cancer has spread to other parts of the body (metastasized). For instance, if cancer spreads to the patient’s liver, then jaundice may appear. In many cases, unfortunately, it is difficult to treat colorectal cancer after it has metastasized.

Cancer or something else?

There are many medical conditions and diseases that lead to jaundice, such as hepatitis. So, jaundice alone may not indicate cancer, although it does indicate that a trip to the doctor is necessary. If jaundice is paired with the following symptom, though, the odds of having colon cancer increase…


In addition to changes in the appearance of bowel movements, some cancer patients also have trouble completely emptying their bowels. For instance, some patients report having a strong urge to release stool. When finished, they feel as though they have not completely released all of their stool, even when they have.

Sometimes, a patient truly has not cleared their bowels, as is the case with symptoms like constipation. Other times, a patient may have actually emptied their bowels yet still feel a strong need “to go.”

What is tenesmus?

The feeling that one must empty the bowels—even after just emptying them—is called tenesmus. Tenesmus is often accompanied by:

  • Cramping
  • Pain
  • Straining

Cancer or something else?

Several diseases and conditions of the bowel can cause tenesmus, including inflammatory bowel disease, Crohn’s disease, and ulcerative colitis. Tenesmus along with other colon cancer symptoms, though, could be an indication of cancer and needs to be discussed with a doctor.

The most common symptom of all?

So, what’s one of the most common—and most troubling—symptoms of colon cancer?…

No Signs

One of the most worrisome aspects of colon cancer? The fact that in many cases there are no noticeable symptoms present at all during the early and even middling stages of the disease. In fact, many patients do not realize they have colon cancer until it’s too late.

What’s the solution?

Cancer is most dangerous in its later stages, after it has spread to other organs and areas of the body. Therefore, physicians recommend regular screenings to help identify the cancer as early as possible. Then, if polyps are detected, they can be removed before they become cancerous. Even if tumors are present, they can still be removed with surgery if caught early enough.

When should people begin screening?

Health experts often encourage patients to have regular screenings for colorectal cancer beginning at age 50. Those with a family history of the cancer should start their screenings a bit earlier. In many cases, these individuals will start screenings around 40 or 10 years earlier than when their first-degree relative was diagnosed.

Don’t skip appointments.

Regular screenings and keeping a lookout for potential warning signs are essential. Why? Because experts estimate that more than half of all colorectal cancers could be prevented or treated if they are caught early enough.

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