Colorectal Cancer Symptoms

Colorectal cancer symptoms can include changes in bowel habits, blood in the stool, abdominal pain, unexplained weight loss, and fatigue. However, colorectal cancer often causes no symptoms in its early stages, which is why screening is important even when you feel healthy.

Colorectal cancer, sometimes called colon cancer or rectal cancer depending on where it begins, develops when abnormal cells in the lining of the colon or rectum grow out of control and form a tumor. “Signs” are changes that can be observed or measured, such as blood in the stool or anemia on a blood test. “Symptoms” are changes you experience, such as pain, fatigue, or changes in bowel movements.

Many colorectal cancer signs can also be caused by conditions that are not cancer, including hemorrhoids, infections, and irritable bowel syndrome. New, persistent, or unexplained symptoms should be discussed with your healthcare provider.

What are the most common colon cancer symptoms?

The most common colon cancer symptoms include a persistent change in bowel habits, rectal bleeding or blood in the stool, abdominal pain or cramping, fatigue, and unintentional weight loss. Some patients may also develop iron-deficiency anemia from slow bleeding in the digestive tract. There is no single symptom that confirms colon cancer, and some people have no symptoms before the disease is found through screening.

Changes in your bowel movements and stool

Changes in your normal bowel habits can be one of the warning signs of colorectal cancer. These may include:

• Constipation or diarrhea that does not go away

• A change in the consistency or shape of your stool

• A feeling that you still need to have a bowel movement after using the bathroom

• Stools that become unusually narrow

A persistent change from what is normal for you should be discussed with your healthcare provider.

Rectal bleeding or blood in the stool

Bleeding from the colon or rectum can appear in different ways:

• Bright red blood in or on the stool

• Dark red or maroon-colored stool

• Very dark or black, tarry stool

Sometimes colorectal cancer causes small amounts of bleeding that cannot be seen. This hidden, or occult, blood may be detected with stool-based tests such as a fecal occult blood test. Blood in the stool should always be discussed with a healthcare provider, even though conditions such as hemorrhoids can also cause rectal bleeding.

Abdominal pain, bloating, or discomfort

A tumor can narrow or partially block the colon, affecting how stool and gas move through the digestive system.

Symptoms can include:

• Persistent abdominal pain or cramping

• Gas or bloating

• A feeling of fullness

• Nausea or vomiting

• A noticeable lump or mass in the abdomen

Severe abdominal pain, significant swelling, vomiting, or an inability to pass stool or gas can be signs of a bowel obstruction and require prompt medical attention.

Unintentional weight loss and fatigue

Some patients experience more general changes in their health, including:

• Unintentional weight loss

• Persistent fatigue

• Weakness

• Loss of appetite

These symptoms are not specific to colorectal cancer, but unexplained changes that persist should be evaluated.

Signs of anemia

Colorectal tumors can bleed slowly over time without causing visible blood in the stool. This blood loss may lead to iron-deficiency anemia.

Symptoms of anemia can include:

• Fatigue

• Weakness

• Pale skin

• Dizziness

• Shortness of breath

In some patients, anemia found during routine blood work may be one of the first clues that leads to further testing.

Are there early symptoms of colon cancer?

Early symptoms of colon cancer may be mild or completely absent. A small tumor or precancerous polyp may not interfere enough with normal bowel function to cause noticeable changes.

This is why symptoms alone cannot reliably tell you whether colorectal cancer is present. Colorectal cancer screening can find cancer before symptoms develop and identify precancerous polyps that can be removed before they become cancer.

Can colorectal cancer symptoms come and go?

Yes. Changes in bowel habits, abdominal discomfort, bloating, or small amounts of rectal bleeding may come and go, particularly early in the disease.

What matters is whether a symptom is new or unusual for you, keeps returning, becomes more frequent, or gets worse over time. Persistent or recurring symptoms should be discussed with your healthcare provider.

Can symptoms depend on where the cancer is in the colon?

Yes. Colon cancer symptoms can vary depending on where a tumor develops.

Cancer on the right side of the colon may cause slow bleeding that is not visible in the stool. Over time, this can contribute to iron-deficiency anemia, fatigue, weakness, or shortness of breath.

Cancer on the left side may interfere with the passage of stool as a tumor grows, causing constipation, changes in stool shape, abdominal cramping, or symptoms of a bowel obstruction.

Rectal cancer may cause rectal bleeding, changes in bowel movements, or a persistent feeling that you still need to have a bowel movement after using the bathroom.

When should patients talk to a doctor about symptoms?

Talk with your healthcare provider if you develop a persistent change in bowel habits, rectal bleeding, blood in your stool, unexplained abdominal pain, fatigue, anemia, or unintentional weight loss. Your doctor may ask about your symptoms and risk factors for colorectal cancer and may refer you to a gastroenterologist, a doctor who specializes in gastroenterology and conditions affecting the digestive system.

How are colon cancer symptoms evaluated and diagnosed?

Having possible signs of colon cancer does not mean you have the disease. Your healthcare provider may review your symptoms, medical and family history, and risk factors and perform a physical exam or order blood and stool tests.

A colonoscopy allows a doctor to examine the inside of the colon and rectum and identify abnormal areas or colon polyps. Tissue samples or polyps can also be removed during the procedure. A colorectal cancer diagnosis is confirmed by examining a tissue sample, called a biopsy, for cancer cells.

Colorectal cancer screening and colonoscopy before symptoms appear

Screening can find precancerous polyps or colorectal cancer before symptoms develop. Finding and removing certain precancerous polyps can also prevent some colorectal cancers from developing.

Screening options include stool-based tests and visual examinations such as colonoscopy. During a colonoscopy, a healthcare provider can examine the entire colon and rectum and remove certain polyps.

The American Cancer Society recommends that people at average risk begin regular colorectal cancer screening at age 45. The appropriate test and screening schedule depend on your individual risk, preferences, and medical history.

Colorectal cancer risk factors and when to start screening

Your risk for colon cancer depends on several factors. People at higher risk may need to begin screening earlier or have testing more frequently.

Risk factors include a personal history of colon cancer or certain colorectal polyps, a family history of colorectal cancer, and inflammatory bowel disease, including Crohn’s disease and ulcerative colitis. Inherited conditions can also increase risk. Familial adenomatous polyposis (FAP) causes numerous adenomatous polyps in the colon and rectum and greatly increases colorectal cancer risk, while Lynch syndrome is another inherited condition associated with increased risk.

If you have an increased risk for colorectal cancer, talk with your healthcare team about when screening should begin.

What should I do if I have colorectal cancer symptoms?

If you are experiencing possible signs of colon cancer, talk with your healthcare provider. Many of these symptoms are caused by conditions other than cancer, but persistent or unexplained changes deserve evaluation.

Do not wait for symptoms before thinking about colorectal cancer screening. Because colon cancer and rectal cancer may not cause noticeable symptoms in their early stages, feeling well does not mean cancer or precancerous polyps are not present.

Following the screening schedule recommended for your individual risk can help find colorectal cancer earlier and identify precancerous polyps before they become cancer.