Colorectal cancer starts in the cells lining your colon or rectum
Colorectal cancer is a disease in which malignant (cancerous) cells form in the inner lining of your colon or rectum. The colon is the large intestine, and the rectum is the final section where stool is stored before leaving your body. Cancer begins when cells in this lining start to grow abnormally and multiply without stopping.
Most colorectal cancers develop slowly over many years. They often start as small, noncancerous growths called polyps. Some polyps can turn into cancer if they are not found and removed. This is why screening—looking for polyps or cancer before you have symptoms—is so important. Catching the disease early, when it is still in the colon or rectum, makes treatment much more effective.
Colorectal cancer can spread to other parts of your body, including the lymph nodes, liver, and lungs. The stage of the cancer—how far it has spread—determines what treatment options are available and what the outlook may be.
Key Takeaways
- Colorectal cancer develops from cells in the lining of the colon or rectum and usually grows slowly over years.
- Most cases begin as polyps, which is why screening can catch the disease before it becomes cancer.
- Risk factors include age over 50, family history, inflammatory bowel disease, and lifestyle factors like smoking and diet.
- Early-stage colorectal cancer often has no symptoms, which is why screening is recommended even when you feel well.
- Treatment options depend on the stage and may include surgery, chemotherapy, radiation, or a combination of these.
Who is at higher risk for colorectal cancer
Your risk increases with age. Colorectal cancer can occur at any age, but it is most common in people over 50. This is why screening is routinely recommended starting at age 45 for average-risk adults, and earlier for those with risk factors.
Family history matters. If a parent, sibling, or child has had colorectal cancer, your risk is higher. The risk is even greater if that relative was diagnosed before age 50 or if multiple family members have had the disease. Inherited genetic conditions like Lynch syndrome and familial adenomatous polyposis (FAP) significantly raise the risk.
Certain medical conditions increase risk, including inflammatory bowel disease (Crohn's disease or ulcerative colitis), type 2 diabetes, and obesity. Lifestyle factors also play a role: smoking, heavy alcohol use, a diet high in red or processed meat, physical inactivity, and a diet low in fiber and vegetables are all associated with higher risk.
Symptoms you might notice, and when they appear
Early-stage colorectal cancer often causes no symptoms at all. This is why screening is so valuable—it can find cancer or precancerous polyps before you feel anything wrong. By the time symptoms appear, the cancer may have already advanced.
When symptoms do occur, they may include a change in bowel habits (diarrhea, constipation, or narrower stools lasting more than a few weeks), blood in or on the stool, persistent abdominal discomfort (cramps, gas, or pain), a feeling that your bowel does not empty completely, weakness or fatigue, or unexplained weight loss.
These symptoms can be caused by many conditions other than cancer, including hemorrhoids, infections, or irritable bowel syndrome. But if you notice any of these changes lasting more than a couple of weeks, it is important to talk with your doctor. Do not assume it is something minor.
How colorectal cancer is found
Screening tests look for polyps or early signs of cancer in people without symptoms. The most common screening method is a colonoscopy, in which a doctor uses a thin, flexible tube with a camera to look inside your entire colon and rectum. If polyps are found, they can be removed during the same procedure. A colonoscopy can both find and treat precancerous growths.
Other screening options include a fecal immunochemical test (FIT), which checks a stool sample for blood, and a high-sensitivity guaiac-based fecal occult blood test (gFOBT), which also looks for hidden blood in stool. Some people use flexible sigmoidoscopy, which examines only the lower part of the colon, or CT colonography (virtual colonoscopy), which uses imaging instead of a camera.
If you have symptoms or screening finds something abnormal, your doctor may order additional tests. A biopsy removes a small tissue sample to check for cancer cells. Imaging tests like CT scans or MRI may be used to see if cancer has spread beyond the colon or rectum.
Stages of colorectal cancer and what they mean
Staging describes how far the cancer has spread and helps doctors plan treatment. Stage 0 means abnormal cells are found only in the innermost lining of the colon or rectum. Stage I means the cancer has grown through the inner lining but has not reached the lymph nodes or distant organs.
Stage II means the cancer has grown through the muscle layer of the colon or rectum wall but has not spread to lymph nodes. Stage III means the cancer has spread to nearby lymph nodes but not to distant organs. Stage IV means the cancer has spread to distant organs like the liver or lungs.
Doctors also describe colorectal cancer by how abnormal the cancer cells look under a microscope (the grade) and whether certain genetic changes are present. These details help predict how fast the cancer may grow and which treatments are most likely to work.
Treatment options depend on stage and location
Surgery is the main treatment for most colorectal cancers. The surgeon removes the section of the colon or rectum that contains the cancer, along with nearby lymph nodes. For early-stage cancers found during screening, removing the polyp may be all that is needed. For more advanced cancers, a larger section must be removed.
Chemotherapy uses drugs to kill cancer cells throughout the body. It may be given before surgery to shrink the tumor, after surgery to destroy any remaining cancer cells, or as the main treatment if surgery is not an option. Radiation therapy uses high-energy beams to kill cancer cells and is sometimes used before or after surgery, especially for rectal cancer.
Newer treatments called targeted therapy and immunotherapy work differently than traditional chemotherapy. They target specific features of cancer cells or help your immune system recognize and attack cancer. These may be options depending on the specific characteristics of your cancer.
What happens after treatment ends
After treatment, you will have follow-up appointments with your doctor to watch for signs that cancer has returned. These visits typically include physical exams and blood tests. Imaging tests or colonoscopy may be done at certain intervals depending on your stage and type of treatment.
Your doctor will discuss a schedule for follow-up care with you. The frequency of visits is usually higher in the first few years after treatment and may decrease over time. It is important to keep these appointments and report any new symptoms right away.
Lifestyle changes can support your health during and after treatment. These may include eating a balanced diet, staying physically active as your doctor recommends, not smoking, limiting alcohol, and managing stress. Your medical team can refer you to nutritionists, counselors, or support groups if you need help with any of these areas.
Frequently Asked Questions
What is the difference between a polyp and colorectal cancer?
A polyp is a growth in the colon or rectum lining. Most polyps are not cancer and never become cancer. However, some types of polyps can develop into cancer over time if not removed. This is why finding and removing polyps during screening is so important—it prevents cancer from developing in the first place.
Can colorectal cancer run in families?
Yes. If a close relative has had colorectal cancer, your risk is higher. The risk is even greater if multiple family members have had it or if it was diagnosed at a young age. Some families carry inherited genetic mutations that significantly raise the risk. Talk with your doctor about your family history so screening can start at the right age for you.
Is colorectal cancer preventable?
You cannot prevent colorectal cancer with certainty, but you can lower your risk. Regular screening is the most effective way to prevent cancer by finding and removing polyps before they become cancerous. You can also reduce risk by not smoking, limiting alcohol, eating a diet high in vegetables and fiber, staying physically active, and maintaining a healthy weight.
What should I do if I have symptoms like blood in my stool?
Contact your doctor. Blood in stool can have many causes, including hemorrhoids or minor tears, but it should always be evaluated by a healthcare provider. Your doctor can examine you and order tests if needed to find out what is causing the symptom. Do not wait or assume it is minor.
How long does colorectal cancer treatment usually take?
Treatment length varies widely depending on the stage, type of treatment, and your individual situation. Surgery may be a single procedure, but recovery takes weeks. Chemotherapy or radiation may continue for several months. Your doctor will explain the expected timeline for your specific treatment plan.