Colon Cancer: Symptoms, Screening, Diagnosis, Treatment and Support
Updated: 2 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026
Quick Answer: What is colon cancer?
Colon cancer is a growth of abnormal cells that begins in the colon, the first and longest part of the large intestine. It often starts as a polyp, and some polyps can become cancer over time. Early colon cancer may cause no symptoms, so screening and professional evaluation are important parts of prevention and care. [4]
What the research says
Removing precancerous polyps is linked to fewer colorectal cancer deaths. In the National Polyp Study, 2,602 people who had adenomas removed during colonoscopy were followed for a median of 15.8 years. Twelve died of colorectal cancer, compared with 25.4 expected deaths estimated from general-population data (standardized incidence-based mortality ratio 0.47, 95% CI 0.26 to 0.80), about a 53% lower rate (Zauber et al., N Engl J Med, 2012). [1]
Sigmoidoscopy screening lowers cancer incidence and deaths in the lower colon. A meta-analysis of 4 randomized trials and 10 observational studies found that screening sigmoidoscopy reduced distal colorectal cancer incidence by 31% (95% CI 26% to 37%) and mortality by 46% (95% CI 33% to 57%) in intention-to-screen analysis, with no clear effect on cancer of the proximal colon. Observational studies suggested that colonoscopy may lower deaths from proximal colon cancer compared with sigmoidoscopy, but this needs more research (Brenner et al., BMJ, 2014). [2]
Randomized evidence that screening extends lifespan is limited. A meta-analysis of randomized trials covering six cancer screening tests (about 2.1 million people) found that, for colorectal screening, only sigmoidoscopy showed a significant lifetime gain: about 110 days (95% CI 0 to 274 days). Colonoscopy (37 days, 95% CI −146 to 146) and fecal occult blood testing (0 days, 95% CI −70.7 to 70.7) did not show a significant difference. These results measure overall lifetime, not cancer-specific outcomes, so personal screening decisions should be made with a healthcare professional (Bretthauer et al., JAMA Intern Med, 2023). [3]
What is colon cancer?
Colon cancer is a growth of cells that begins in the colon. The colon is the first and longest part of the large intestine, which is the final part of the digestive system. [4]
Colon cancer often begins as small clumps of cells called polyps inside the colon. Polyps generally are not cancerous, but some can turn into cancer over time. Polyps often do not cause symptoms, which is why screening can be useful. [4]
Colon cancer is sometimes called colorectal cancer. That broader term includes cancer that begins in the colon and cancer that begins in the rectum. [4]
Colon cancer at a glance
Topic | Key information |
Definition | A cancer that begins in the cells of the colon. |
Early course | It often begins as a polyp and may cause no symptoms at first. |
Possible symptoms | Bowel-habit changes, blood in stool, abdominal discomfort, incomplete emptying, tiredness and unexplained weight loss. |
Screening | Screening can find polyps and early disease; timing depends on average or increased risk. |
Diagnosis | Colonoscopy, biopsy, blood tests and imaging may be used. [6] |
Treatment | May include surgery, chemotherapy, radiation, targeted therapy, immunotherapy and palliative care. |
Next step | Discuss lasting symptoms and personal screening needs with a healthcare professional. |
What symptoms can colon cancer cause?
Early-stage colon cancer may not cause any symptoms. When symptoms appear, they may depend on the size of the cancer and where it is located in the colon. [4]
Possible symptoms include:
A change in bowel habits, such as more-frequent, looser stools or diarrhea, constipation, or changes in stool shape.
Rectal bleeding or blood in the stool.
Ongoing discomfort in the abdomen, including cramps, gas or pain.
A feeling that the bowel does not empty completely during a bowel movement.
Weakness or tiredness, which iron deficiency anemia can cause.
Losing weight without trying. [4]
These symptoms can have causes other than colon cancer. [4] An online article cannot determine the cause of an individual symptom.
When should you see a healthcare professional?
Make an appointment with a healthcare professional if you notice lasting symptoms that worry you, including blood in the stool, rectal bleeding, ongoing bowel changes, abdominal discomfort or unexplained weight loss. Lasting symptoms need professional assessment.
Early colon cancer may have no symptoms. Do not use the absence of symptoms to decide whether screening is appropriate for you. Screening timing depends on risk and factors such as age, family history and other health risks.
What causes colon cancer?
Healthcare professionals are not certain what causes most colon cancers. The disease begins when cells in the colon develop changes in their DNA. [4]
DNA holds instructions that tell cells what to do. Changes can cause cells to multiply quickly and continue living when healthy cells would normally die. The extra cells can form polyps, and a cancerous polyp can invade deeper into the colon wall and later spread to other parts of the body. [4]
When cancer spreads to other parts of the body, it is called metastatic cancer. [4]
What are the risk factors for colon cancer?
Colon cancer risk can be raised by a number of different factors.
Risk factor | What to know |
Age | Colon cancer can occur at any age, but most people with it are older than 50. [4] |
Race | Black people in the United States have a greater risk than people of some other races. [4] |
Personal history | Previous colorectal cancer or polyps increases risk. [4] |
Inflammatory bowel disease | Ulcerative colitis and Crohn’s disease can increase risk. [4] |
Inherited syndromes | Familial adenomatous polyposis and Lynch syndrome are inherited syndromes linked to increased risk. [4] |
Family history | Having a blood relative with colon cancer increases risk, especially with more than one affected family member. [4] |
Lifestyle and health factors | Physical inactivity, obesity and diabetes may increase risk. [4] |
Smoking and alcohol | Smoking and drinking alcohol can increase risk. [4] |
Dietary pattern | A low-fiber, high-fat pattern may be linked with higher risk; research on some foods is mixed. [4] |
Previous radiation | Abdominal radiation therapy for an earlier cancer increases risk. [4] |
A risk factor does not prove that someone will develop colon cancer. People without a listed risk factor can still develop the disease.
How can you reduce your risk of colon cancer?
You can reduce your risk of colon cancer by discussing screening, eating a varied diet, limiting alcohol, not smoking, staying active and working toward a healthy weight.
Discuss screening. People at average risk may be advised to consider screening around age 45, while people at increased risk may need to start sooner. [4] Discuss timing and options with your healthcare team.
Eat a varied diet. Include fruits, vegetables and whole grains for fiber and nutrients.
Limit alcohol. If you drink, keep within the limits recommended by your healthcare professional.
Do not smoke. If you smoke, ask your healthcare team about quitting support.
Stay physically active. Aim for regular activity and build up gradually if you have been inactive.
Work toward a healthy weight. Ask for professional guidance about safe, gradual weight loss if needed.
What about aspirin or other preventive medicines?
Some evidence links regular aspirin or aspirin-like medicines with a lower risk of polyps and colon cancer. However, the appropriate dose and duration are unclear, and daily aspirin can cause ulcers and digestive bleeding. [4]
These medicines are generally reserved for people at high risk. [4] Do not start aspirin for cancer prevention without discussing your individual risks and benefits with a healthcare professional.
How is colon cancer screened and diagnosed?
Colon cancer can be found during routine screening and is typically diagnosed with a biopsy during a colonoscopy, while blood tests can offer clues about overall health. [6]
Colonoscopy
A colonoscopy uses a long, flexible tube with a camera to view the whole colon. [4][6] During the procedure, a healthcare professional may remove polyps or collect tissue samples. [6]
Removing a polyp can both provide tissue for testing and potentially prevent a polyp from becoming cancer. Your healthcare team can explain the preparation, benefits and risks of the test.
Biopsy
A biopsy removes a tissue sample for laboratory testing. The sample is often collected during a colonoscopy, although, more rarely, surgery may be needed. [6]
Laboratory tests can show whether cells are cancerous. The healthcare team uses the results to understand the prognosis and create a treatment plan. [6]
Blood tests
Blood tests can provide clues about overall health, including kidney and liver function, and may show a low red-blood-cell level that could indicate the cancer is causing bleeding. [6]
Colon cancer sometimes makes a protein tumor marker called carcinoembryonic antigen, or CEA. CEA blood tests may be used over time to help track treatment response or detect possible recurrence after treatment. [6]
Imaging after diagnosis
After diagnosis, imaging tests can help find out whether the cancer has spread. CT scanning is the main imaging test, and MRI, X-rays or ultrasound also may help. Details of the stage may not be known until after surgery to remove the cancer. [6]
Your care team will explain the stage of the cancer, which helps plan treatment.
How is colon cancer treated?
Treatment often involves surgery to remove the cancer. Other options may include radiation, chemotherapy, targeted therapy, immunotherapy and palliative care. Treatment depends on the cancer’s size and location, your genes and your health history. [5]
Treatment | General role |
Polyp removal | May remove a very small cancer contained within a polyp. [5] |
Minimally invasive surgery | Removes the cancer through several small incisions. [5] |
Partial colectomy | Removes the part of the colon containing the cancer and nearby tissue. [5] |
Ostomy | Creates an opening so stool can leave the body through a pouch when the colon cannot be reconnected immediately or permanently. [5] |
Chemotherapy | May be used before or after surgery, with radiation, or when surgery is not an option. [5] |
Radiation therapy | May be used before, during or after surgery, to ease symptoms or with chemotherapy. [5] |
Targeted therapy | May be an option for some people, based on the cancer’s genetic changes. [5] |
Immunotherapy | May be used for cancer linked to certain genes or for advanced or metastatic colon cancer. [5] |
Palliative care | Focuses on relieving symptoms and improving quality of life during serious illness. [5] |
Surgery for early colon cancer
A small cancer that has not spread beyond the colon may be removed through a polypectomy during a colonoscopy or through endoscopic mucosal resection. [5] Minimally invasive surgery may be used for polyps that cannot be removed during colonoscopy.
Surgery for more advanced colon cancer
If a cancer has grown into or through the colon, a surgeon may recommend a partial colectomy. Samples of nearby lymph nodes are also tested to see whether the cancer has spread. [5]
Sometimes the healthy sections of the colon or rectum can be reconnected. If they cannot be reconnected, an ostomy may allow stool to leave the body through an opening in the abdomen and into a pouch. An ostomy can sometimes be reversed, but it may be permanent in other situations. [5]
When surgery cannot remove the cancer, an operation may sometimes relieve symptoms such as blockage, bleeding or pain. [5]
Surgery for cancer that can't be removed
When it’s not possible to remove the cancer with surgery, a surgeon might try to relieve symptoms rather than cure the cancer. This surgery can remove colon blockages and ease symptoms, such as bleeding or pain. [5]
Sometimes the cancer has spread only to the liver or lung in someone who is otherwise healthy. Surgery or other localized treatments might remove the cancer. Chemotherapy might be used before or after this type of procedure. This approach provides a chance to be free of cancer over the long term. [5]
Chemotherapy
Chemotherapy uses strong medicines to kill cancer cells. It may be given after surgery to kill any cancer cells that may be left, before surgery to shrink a large cancer so it is easier to remove, or when surgery is not an option. Chemotherapy may sometimes be used with radiation therapy. [5]
Radiation therapy
Radiation therapy uses powerful energy beams to kill cancer cells. It may be used before, during or after surgery, to ease symptoms, or at the same time as chemotherapy. [5]
Targeted therapy and immunotherapy
Targeted therapy uses medicines that attack specific chemicals in cancer cells. To use it, doctors need to understand the genetic changes that contributed to the cancer. [5]
Immunotherapy uses medicine that helps the immune system kill cancer cells. It may be used if the cancer is associated with certain genes or is advanced or metastatic. [5]
What is palliative care?
Palliative care focuses on relieving pain and other symptoms of a serious illness. It is provided by a team that may include doctors, nurses and other trained professionals. [5]
Palliative care can be an extra layer of support during cancer treatment. It may help improve quality of life for people with cancer and their families. [5]
How can people cope with colon cancer?
A colon cancer diagnosis can be difficult to cope with, but information and support can help. Learning enough about the cancer may help you take part in treatment decisions. [5] Support may include:
Asking the healthcare team about the cancer’s type, stage, treatment options and possible side effects.
Staying close to friends and family who can provide practical and emotional support.
Talking with a trusted person, counselor, medical social worker, clergy member or support group.
Asking the healthcare team about support groups in your area. [5]
Requesting information in clear, understandable language.
How can you prepare for an appointment?
If you have colon cancer, you may meet specialists such as a gastroenterologist, oncologist, surgeon or radiation oncologist. Bring or write down: [5]
Your symptoms and when they began.
Other health conditions and family medical history.
All medicines, vitamins and supplements, including doses.
Your most important questions.
A trusted friend or family member, if helpful.
Questions to consider asking:
Where in the colon is the cancer?
What is the stage?
Can you explain the laboratory report?
Has the cancer spread?
Will more tests be needed?
What treatments are available?
What side effects could occur?
How could treatment affect daily life?
How much time is available to decide about treatment?
Frequently asked questions
What is colon cancer?
Colon cancer is a growth of abnormal cells that begins in the colon. It often begins as a polyp, and some polyps can become cancer over time.
What are the early symptoms of colon cancer?
Colon cancer may have no symptoms early on. Possible symptoms include bowel-habit changes, blood in the stool or rectal bleeding, abdominal discomfort, incomplete bowel emptying, tiredness and unexplained weight loss.
Can colon cancer have no symptoms?
Yes. Many people do not have symptoms at first. Screening can help find polyps or cancer before symptoms appear.
What causes colon cancer?
The cause of most colon cancers is not certain. The disease develops when colon cells acquire DNA changes that cause excess growth and continued survival.
When should colon cancer screening begin?
People at average risk may consider starting screening around age 45, while people at increased risk may need to begin sooner. Discuss the timing and test options that fit your health and risk factors with a healthcare professional.
How is colon cancer diagnosed?
Diagnosis may include colonoscopy, biopsy, blood tests and imaging. [6] Blood tests do not diagnose colon cancer but may provide health information or help track CEA over time.
How is colon cancer treated?
Treatment depends on location, stage, overall health and preferences. Options may include surgery, chemotherapy, radiation, targeted therapy, immunotherapy and palliative care.
Can colon cancer be prevented?
Removing some polyps can help prevent colon cancer. Screening, regular physical activity, not smoking, limiting alcohol, eating fruits, vegetables and whole grains, and maintaining a healthy weight may help reduce risk.
When should you see a doctor about colon symptoms?
Make an appointment if you notice lasting symptoms that worry you, including blood in the stool, rectal bleeding, ongoing bowel changes, abdominal discomfort or unexplained weight loss. Only professional evaluation can determine the cause.
Conclusion: what to remember about colon cancer
Colon cancer often begins as a polyp and may not cause symptoms early on. Screening can help find polyps before they become cancer, while professional testing helps determine whether cancer is present and how far it has spread.
Treatment depends on location, stage, overall health and personal preferences. Options may include surgery, chemotherapy, radiation, targeted therapy, immunotherapy and palliative care. If you have lasting symptoms or questions about screening, make a plan with your healthcare team rather than relying on a general article.
Related Reading
Learn more in our guide to Hemicolectomy: Right vs. Left Colon Surgery, Procedure, Risks and Recovery.
Ileostomy: Types, Surgery, Recovery, Stoma Care and Reversal explains when an ileostomy is needed, the loop and end types, what happens during surgery, recovery and reversal.
Lower Endoscopy: Colonoscopy vs. Sigmoidoscopy, Prep, Procedure and Recovery explains how colonoscopy and sigmoidoscopy look inside the colon and rectum to find polyps and cancer.
Learn more in our guide to Low Anterior Resection (LAR): Rectal Cancer Surgery, Risks and Recovery.
Colonoscopy: Purpose, Prep, Procedure, Results and Risks: A colonoscopy screens for colorectal cancer from age 45 and can remove precancerous polyps before they turn into cancer.
Learn more in our guide to Flexible Sigmoidoscopy: Prep, Procedure, Results and Risks.
Virtual Colonoscopy (CT Colonography): Prep, Procedure, Accuracy and Results explains the CT scan that screens the colon for polyps and cancer.
Fecal Occult Blood Test (FOBT): Types, Preparation, Results and Next Steps explains the stool test that checks for hidden bleeding linked to this condition.
Learn more in our guide to Colorectal Cancer Screening: When to Start, Test Options and What Results Mean.
Stool Test: Types, How to Collect a Sample and What Results Mean explains the stool tests used to find infections, bleeding and other gut problems.
Biomarker Testing for Cancer: What It Is, How It Works and What Results Mean explains how testing a tumor for gene changes and proteins helps match people with cancer to the treatments most likely to work.
CEA Test (Carcinoembryonic Antigen): Normal Levels, High Results and Limits explains the tumor marker blood test used to monitor this cancer.
References
Zauber AG, Winawer SJ, O’Brien MJ, et al. Colonoscopic polypectomy and long-term prevention of colorectal-cancer deaths. N Engl J Med. 2012;366(8):687-696. PMID 22356322. https://doi.org/10.1056/NEJMoa1100370
Brenner H, Stock C, Hoffmeister M. Effect of screening sigmoidoscopy and screening colonoscopy on colorectal cancer incidence and mortality: systematic review and meta-analysis of randomised controlled trials and observational studies. BMJ. 2014;348:g2467. PMID 24922745. https://doi.org/10.1136/bmj.g2467
Bretthauer M, Wieszczy P, Løberg M, et al. Estimated lifetime gained with cancer screening tests: a meta-analysis of randomized clinical trials. JAMA Intern Med. 2023;183(11):1196-1203. PMID 37639247. https://doi.org/10.1001/jamainternmed.2023.3798
Mayo Clinic Staff. Colon cancer symptoms & causes. Mayo Clinic. Updated September 10, 2026. https://www.mayoclinic.org/diseases-conditions/colon-cancer/symptoms-causes/syc-20353669
Mayo Clinic Staff. Colon cancer treatment. Mayo Clinic. Updated September 10, 2026. https://www.mayoclinic.org/diseases-conditions/colon-cancer/treatment/drc-20353674
Mayo Clinic Staff. Colon cancer diagnosis & tests. Mayo Clinic. Updated September 10, 2026. https://www.mayoclinic.org/diseases-conditions/colon-cancer/diagnosis-tests/drc-20606101
Disclaimer
This article is for general educational purposes and is not a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition.
It does not diagnose cancer, set an individual screening schedule or recommend a personal treatment plan. Lasting or worrying symptoms require assessment by a qualified healthcare professional.
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