Colorectal cancer refers to cancer that develops in the colon or rectum. Most cases are adenocarcinomas, meaning they arise from the lining of the large intestine or rectum.
This type of cancer often begins as a polyp, a small growth that forms on the surface of the intestinal or rectal lining. As the disease progresses, the tumor may invade the wall of the intestine or rectum and can spread to nearby lymph nodes. Because blood from the intestines flows to the liver, the cancer may eventually spread there after reaching the lymph nodes.
Colorectal cancer is among the most common cancers in Western countries and is the second leading cause of cancer-related deaths. The risk begins to increase significantly between the ages of 40 and 50. Improved screening and earlier diagnosis have contributed to a steady decline in death rates in recent decades.
Risk Factors
Several factors can increase a person’s likelihood of developing colorectal cancer. Individuals with a family history of the disease face a higher risk. Certain inherited disorders are also linked to colorectal cancer, including familial adenomatous polyposis, Lynch syndrome, Peutz-Jeghers syndrome, juvenile polyposis syndrome, and MUTYH polyposis syndrome.
People who have ulcerative colitis or Crohn disease affecting the colon are also at increased risk. Diet can play a role as well, particularly diets high in fat, animal protein, and refined carbohydrates but low in fiber.
For example, individuals with Lynch syndrome, caused by an inherited gene mutation, have a 70–80% lifetime risk of developing colorectal cancer, often before age 50. They may also be at increased risk for other cancers, including endometrial and ovarian cancer.
Another rare genetic condition, MUTYH polyposis syndrome, results from mutations in the MUTYH gene and can lead to colorectal cancer, often beginning in a person’s 60s. People with this syndrome may also develop other types of cancer affecting the digestive tract, bones, ovaries, bladder, thyroid, or skin.
Symptoms
Colorectal cancer typically develops slowly and may not cause noticeable symptoms for a long period. The symptoms depend on the tumor’s location, size, and extent.
Fatigue and weakness can occur due to hidden bleeding in the digestive tract. Many colon cancers bleed gradually, and the blood may not be visible in the stool.
Tumors located in the left side of the colon may cause earlier blockage because the colon is narrower and stool is more solid. This can lead to symptoms such as cramp-like abdominal pain, severe pain, or constipation.
Tumors on the right side of the colon usually cause obstruction later because the colon is wider and its contents are more liquid. As a result, these tumors may grow larger before they are discovered.
The most common early symptom of rectal cancer is bleeding during bowel movements. Even when a person has conditions such as hemorrhoids or diverticular disease, doctors must still consider the possibility of cancer if rectal bleeding occurs. Other symptoms may include painful bowel movements or a feeling that the rectum has not been completely emptied.
Diagnosis
When symptoms suggest colorectal cancer or screening results are abnormal, further testing is required to confirm the diagnosis. A colonoscopy is commonly used to examine the colon and rectum. During the procedure, doctors can remove growths or take tissue samples to determine whether they are cancerous.
If cancer is confirmed, doctors may perform CT scans of the chest, abdomen, and pelvis along with laboratory tests to determine whether the disease has spread and to assess the patient’s overall condition.
Blood tests are not used to diagnose colorectal cancer but can help monitor treatment. For instance, doctors may measure the level of the tumor marker carcinoembryonic antigen (CEA) before and after surgery to track possible recurrence.
Genetic testing may also be performed to identify inherited conditions such as Lynch syndrome or MUTYH polyposis syndrome.
Treatment
Treatment for colorectal cancer usually involves surgery to remove the cancerous section of the intestine along with nearby lymph nodes. In many cases, the remaining parts of the intestine are then reconnected.
Additional treatments may include chemotherapy, radiation therapy, or both, depending on the stage and spread of the cancer. These therapies may help improve survival after surgical removal of visible tumors.
For rectal cancer, surgery depends on the tumor’s location and how deeply it has invaded the rectal wall. In some cases, the rectum and anus must be removed, requiring a permanent colostomy, which creates an opening in the abdominal wall for waste to pass into a collection bag.
If cancer has spread widely, surgery alone may not cure the disease. However, treatments such as chemotherapy may shrink tumors and help extend life.
Prognosis
The chances of cure are highest when colorectal cancer is detected early, before it spreads.
When the cancer is confined to the lining of the bowel wall, the five-year survival rate is about 90%. If it has spread through the bowel wall, survival rates drop to around 73–74%, and when the cancer has spread to other organs, the survival rate falls to less than 20%.
Prevention
Preventing colorectal cancer focuses largely on screening and lifestyle changes. Screening tests help detect polyps or cancer early, often before symptoms develop.
Lifestyle habits may also reduce risk. These include increasing physical activity, maintaining a healthy weight, limiting alcohol intake, avoiding tobacco, eating less red and processed meat, and consuming more fiber from fruits, vegetables, and whole grains.
In some adults between the ages of 50 and 59 who have an increased risk of heart disease, doctors may recommend low-dose aspirin, which may help prevent both heart disease and colorectal cancer.
