Colon cancer occurs when cancerous cells develop in the colon (large intestine). This condition can cause no symptoms, especially at first, but eventually, signs include changes in bathroom habits and blood in stools.
Colon cancer is relatively common and affects people of all genders. The American Cancer Society estimated that more than 100,000 new cases would be diagnosed in the United States in 2024. Proper diagnosis is critical; the sooner it is detected and treated, the better the outcome.
This article discusses colon cancer development, symptoms, treatment, and the factors influencing outcomes.
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Colon Cancer vs. Colorectal Cancer
Though colon and colorectal cancer symptoms can overlap, there are differences between the two cancers. Colon cancer occurs within the colon, whereas colorectal cancer starts in the rectum, which is at the bottom end of the colon that holds stool until you move your bowels.
First Symptoms of Colon Cancer: How to Tell
One of the biggest challenges in diagnosing and managing colon cancer is that early symptoms are not unique to colon cancer and may resemble those of other conditions, such as hemorrhoids, irritable bowel syndrome (IBS), and inflammatory bowel disease (IBD), making it more difficult to detect.
Signs of colon cancer depend on how advanced the disease is. Early signs of colon cancer often go unnoticed until more apparent symptoms develop over time.
Stool Changes and Bleeding
Common early colon cancer symptoms involve changes to your stools (poop) and bathroom habits. The symptoms often last for at least several days and include the following:
- Bloody stools, appearing black or dark brown
- Constipation (difficulty passing stools or passing fewer than three stools a week)
- Diarrhea (loose, watery stools)
- Rectal bleeding (bright red blood when you use the bathroom)
- Skinny stools
Tenesmus
Another sign of colon cancer is tenesmus—the feeling that you need to move your bowels, even when they are empty. Tenesmus may cause pain, discomfort, cramping, and excessive straining.
Abdominal Pain
Cramping and abdominal (belly) pain are symptoms associated with various conditions, such as Crohn's disease or ulcerative colitis. However, they can also accompany colon cancer, causing feelings of gas, bloating, and uncomfortable fullness.
Other Symptoms
Nausea that may lead to vomiting is another sign of colon cancer. As the disease persists, more systemic symptoms emerge. Among these are feelings of fatigue (extreme tiredness) and a lack of energy. Further symptoms may include unexplained weight loss and anemia—low red blood cell count due to bleeding.
Progressive Symptoms and Complications
As colon cancer progresses, it can lead to several complications. These include:
- Jaundice (characterized by yellowing of the whites of the eyes or skin)
- Bowel obstruction (blockage)
- Enlarged liver
- Breathing difficulties
When to Screen for Colon Cancer
According to the American Cancer Society (ACS), adults with an average cancer risk should start regular screening (either stool-based tests or visual exams) for this cancer beginning at 45 until they’re 75. From age 76 to 85, the choice to test is based on your overall health status, life expectancy, and personal preference. The ACS doesn’t recommend testing for those 86 or older.
How Colon Cancer Develops
Cancer occurs when the DNA of healthy colon cells changes, causing gene mutations. Affected genes include oncogenes, which regulate cell division, and tumor suppressors, which break down and “recycle” old cells. As oncogene activity increases and tumor-suppressing genes slow down, cells multiply rapidly and spread, forming cancerous growths.
You can inherit the mutations that cause cancer cells from your biological parents (germline mutations), or mutations can result from environmental factors—the more common cause. Several health factors raise the risk of colon cancer:
- A diet high in fats, red meat, or processed meats
- Age over 45
- Alcohol use
- Colorectal polyps
- Excess weight or having obesity
- Family history of colorectal cancer
- IBD
- Insufficient fiber, fresh fruit, or vegetables
- Smoking
Polyp or Tumor Location
The colon is the final part of the digestive system. It is a 5-foot-long tube that connects the small intestine to the anus. The colon's five major parts are:
- The cecum, which is the entry point from the small intestine
- The ascending colon, which travels upward from the cecum
- The transverse colon, which crosses the abdomen from right to left
- The descending colon, which travels downward
- The sigmoid colon, which travels back to the center of the body
Colon cancer cells appear first in the membranes lining the colon before eventually moving to adjacent and sometimes distant parts of the body. Sometimes noncancerous growths, or polyps, as well as precancerous polyps, can develop into cancer.
Prognosis of Colon Cancer at Diagnosis and After Treatment
The prognosis of colon cancer depends on how deeply the cancer cells have grown in your colon and how far the cancer has spread at the time of diagnosis. Generally, the outcomes are better if the cancer is limited to the colon. It becomes much more challenging to treat and manage in later stages after spreading to nearby lymph nodes, surrounding tissues, or other body parts.
Cancer Stages
Healthcare providers stage colon cancer based on how far it has spread. Stages range from 0 to 4; here’s a breakdown:
- Stage 0: Presence of abnormal or precancerous cells in the inner colon lining
- Stage 1: The cancerous cells spread outside the inner lining but remain in the colon
- Stage 2: The cancer spreads outside the colon but hasn’t reached the lymph nodes
- Stage 3: The cancer spreads outside of the colon and affects the lymph nodes
- Stage 4: Also known as metastatic colon cancer, cancer cells spread to affect distant parts of the body
Colon cancers caught in earlier stages are more treatable. For instance, 80% to 95% of those with cancer detected at stage 1 are alive five years later; this drops to about 15% for stage 4. Therapies may be ineffective with end-stage colon cancer.
Treatment to Remove Colon Cancer
There are several treatments for colon cancer. Healthcare providers determine their approach to each case by considering the cancer's stage and the individual's overall health. Therapies for colon cancer include surgery, chemotherapy, radiation therapy, and medications.
Minimally Invasive Options
For cancer confined to the inner lining of the colon, a colonoscopy can remove these tumors and cure early cancer. For more invasive but early-stage cancer, providers use minimally invasive methods (e.g., laparoscopic surgery) to remove tumors, affected tissues, or lymph nodes.
Colectomy
Acolectomyis a surgery that involves removing the part of the colon with the cancerous tumor (or precancerous polyps), surrounding tissues, and lymph nodes.
While there are risks associated with this surgery, such as excess bleeding, infection, or injury to surrounding organs, it has a high success rate. People with stage 1 colon cancer experience a 94% success rate, while those with stage 4 experience a 50% success rate with colectomy.
Radiation Therapy
Cancer specialists, known as oncologists, typically recommend radiation therapy alongside surgery. Radiation therapy involves directing radiation to the affected areas to kill cancer cells. This therapy causes a wide range of side effects, including skin irritation, slow wound healing, nausea, incontinence, diarrhea, pain, and others.
The success of radiation therapy depends on the cancer stage and the specific method used. It ranges from 15% to 91% in five years.
Chemotherapy
Healthcare providers may try chemotherapy, an intravenous (IV) or oral medication that targets cancer cells, alongside surgery. The side effects of chemotherapy include hair loss, mouth sores, weight loss, nausea, diarrhea, and changes in nail growth, among others. Research evidence suggests chemotherapy is best for stage 3 or higher cancers.
Targeted Therapy
Certain medications that stimulate the immune system and target cancer cells can also play a role in therapy. Drugs that treat this condition include Avastin (bevacizumab), Cyramza (ramucirumab), and Zaltrap (ziv-aflibercept). Side effects include bleeding from the rectum, headaches, high blood pressure, and protein in the urine.
Immunotherapy
Immunotherapy involves medications that stimulate immune function to combat cancer cells. Immunotherapy drugs like Keytruda (pembrolizumab), Opdivo (nivolumab), and Yervoy (ipilimumab) are given via IV every two to four weeks. These therapies may cause itching, fever, chills, dizziness, and wheezing. Researchers found cure rates ranging from 18.6% to 43.8% at two years.
Recurrence After Treatment
Even with successful surgery or other treatments, there’s a chance that colon cancer can come back. Overall, researchers have found that about 14.6% of those who receive surgery experience recurrence within five years. However, the chances of the cancer coming back also depend on how advanced it is. Stage 1 colon cancer had a five-year recurrence rate of 7%, which rose to 20% for stage 3 cancer.
Statistics on Life Expectancy
How long someone survives after a colon cancer diagnosis depends on how advanced the cancer is. According to data from 2016 compiled by the National Cancer Institute, the five-year survival rate for colon cancer is 64.9%. Across all stages of cancer, this means nearly two-thirds of those diagnosed are expected to survive at least five years.
Summary
Colon cancer affects the colon (large intestine) and causes a range of symptoms, including changes in the stool and abdominal pain. This cancer often doesn’t cause issues at first, which is why healthcare providers recommend that adults over 45 or at increased risk have regular screening for early detection.
Treatments for colon cancer depend on the cancer stage and include surgery, radiation therapy, chemotherapy, and other approaches. In about 20% of cases, the cancer returns following surgery or other treatment. Overall, about two-thirds of those diagnosed survive five or more years.
