Colon cancer (also known as Colorectal cancer (CRC), bowel cancer and colon cancer) is cancer of the large intestine (colon), which is the final part of your digestive tract. Most cases of colon cancer begin as small, noncancerous (benign) clumps of cells called adenomatous polyps. Over time some of these polyps can become colon cancers.
Polyps may be small and produce few, if any, symptoms. For this reason, doctors recommend regular screening tests to help prevent colon cancer by identifying and removing polyps before they turn into cancer.
Normally, body cells follow an orderly process of growth, division, and death. Cancer happens when cells grow and divide uncontrollably, without dying.
Most colon cancer originates from noncancerous, or benign, tumors called adenomatous polyps that form on the inner walls of the large intestine.
Cancerous cells may spread from malignant tumors to other parts of the body through the blood and lymph systems.
These cancer cells can grow and invade healthy tissue nearby and throughout the body, in a process called metastasis. The result is a more serious, less treatable condition.
The exact causes are unknown, but colon cancer has several potential risk factors.
Inflammatory bowel disease
People with inflammatory bowel disease (ulcerative colitis and Crohn’s disease) are at increased risk of colon cancer. The risk increases the longer a person has the disease, and the worse the severity of inflammation. In these high risk groups, both prevention with aspirin and regular colonoscopies are recommended. People with inflammatory bowel disease account for less than 2% of colon cancer cases yearly. In those with Crohn’s disease 2% get colorectal cancer after 10 years, 8% after 20 years, and 18% after 30 years. In those with ulcerative colitis approximately 16% develop either a cancer precursor or cancer of the colon over 30 years.
Colon cancer usually derives from precancerous polyps that exist in the large intestine.
The most common types of polyps are:
- Adenomas: These can resemble the normal lining of the colon but look different under a microscope. They can become cancerous.
- Hyperplastic polyps: Colon cancer rarely develops from hyperplastic polyps, as they are typically benign.
Some of these polyps may grow into malignant colon cancer over time, if they are not removed during the early stages of treatment.
Traits, habits, and diet
Age is an important risk factor for colon cancer. Around 91 percent of those who receive a diagnosis are over 50 years old.
Colon cancer is more likely in people with sedentary lifestyles, those with obesity, and those who smoke tobacco.
As the colon is part of the digestive system, diet is an important factor. Diets that are low in fiber and high in fat, calories, red meat, alcohol, and processed meats have been linked to a higher risk of colon cancer.
Those with a family history in two or more first-degree relatives (such as a parent or sibling) have a two to threefold greater risk of disease and this group accounts for about 20% of all cases. A number of genetic syndromes are also associated with higher rates of colorectal cancer. The most common of these is hereditary nonpolyposis colorectal cancer (HNPCC or Lynch syndrome) which is present in about 3% of people with colorectal cancer. Other syndromes that are strongly associated with colorectal cancer include Gardner syndrome, and familial adenomatous polyposis (FAP). For people with these syndromes, cancer almost always occurs and makes up 1% of the cancer cases. A total proctocolectomy may be recommended for people with FAP as a preventative measure due to the high risk of malignancy. Colectomy, removal of the colon, may not suffice as a preventative measure because of the high risk of rectal cancer if the rectum remains.
Signs and symptoms of colon cancer include:
- A change in your bowel habits, including diarrhea or constipation or a change in the consistency of your stool, that lasts longer than four weeks
- Rectal bleeding or blood in your stool
- Persistent abdominal discomfort, such as cramps, gas or pain
- A feeling that your bowel doesn’t empty completely
- Weakness or fatigue
- Unexplained weight loss
Many people with colon cancer experience no symptoms in the early stages of the disease. When symptoms appear, they’ll likely vary, depending on the cancer’s size and location in your large intestine.
When to see a doctor
If you notice any symptoms of colon cancer, such as blood in your stool or an ongoing change in bowel habits, do not hesitate to make an appointment with your doctor.
Talk to your doctor about when you should begin screening for colon cancer. Guidelines generally recommend that colon cancer screenings begin at age 50. Your doctor may recommend more frequent or earlier screening if you have other risk factors, such as a family history of the disease.
Colon Cancer Stages
There are different ways of staging cancer. The stages depend on how far the cancer has spread.
Here is a brief summary of a commonly used four-stage account of where the cancer is at the beginning of each stage.
Stage 0: The cancer is in a very early stage. It is known as carcinoma in situ. It has not grown further than the inner layer of the colon.
Stage 1: The cancer has grown into the next layer of tissue, but it has not reached the lymph nodes or other organs.
Stage 2: The cancer has reached the outer layers of the colon, but it has not spread beyond the colon.
Stage 3: The cancer has grown through outer layers of the colon and it has reached one to three lymph nodes. It has not spread to distant sites.
Stage 4: The cancer has reached other tissues beyond the wall of the colon. As stage 4 progresses, the cancer reaches distant parts of the body.
Cancer develops progressively. Each stage is not fixed but describes a phase during which certain developments take place.
Treatment for Colon Cancer
Surgery is the most common initial medical treatment for colorectal cancer. During surgery, the tumor, a small margin of the surrounding healthy intestine, and adjacent lymph nodes are removed. The surgeon then reconnects the healthy sections of the bowel. In patients with rectal cancer, the rectum sometimes is permanently removed if the cancer arises too low in the rectum. The surgeon then creates an opening (colostomy) on the abdominal wall through which solid waste from the colon is excreted. Specially trained nurses (enterostomal therapists) can help patients adjust to colostomies, and most patients with colostomies return to a normal lifestyle.
For early colon cancers, the recommended treatment is surgical removal. For most people with early stage colon cancer (stage I and most stage II), surgery alone is the only treatment required. Chemotherapy may be offered to some people with stage II cancers who have factors suggesting that their tumor may be at higher risk of recurrence. However, once a colon cancer has spread to local lymph nodes (stage III), the risk of the cancer returning remains high even if all visible evidence of the cancer has been removed by the surgeon. This is due to an increased likelihood that tiny cancer cells may have escaped prior to surgery and are too small to detect at that time by blood tests, scans or even direct examination. Their presence is deduced from higher risk of recurrence of the colon cancer at a later date (relapse). Medical cancer doctors (medical oncologists) recommend additional treatments with chemotherapy in this setting to lower the risk of the cancer’s return. Drugs used for chemotherapy enter the bloodstream and attack any colon cancer cells that were shed into the blood or lymphatic systems prior to the operation, attempting to kill them before they set up shop in other organs. This strategy, called adjuvant chemotherapy, has been proven to lower the risk of cancer recurrence and is recommended for all patients with stage III colon cancer who are healthy enough to undergo it, as well as for some higher risk stage II patients whose tumor may have been found to have obstructed or perforated the bowel wall prior to surgery.
There are several different options for adjuvant chemotherapy for the treatment of colon cancer. The treatments involve a combination of chemotherapy drugs given orally or into the veins. The treatments typically are given for a total of six months. It is important to meet with an oncologist who can explain adjuvant chemotherapy options as well as side effects to watch out for so that the right choice can be made for a patient as an individual.
Chemotherapy usually is given in a health care professional’s clinic, in the hospital as an outpatient, or at home. Chemotherapy usually is given in cycles of treatment followed by recovery periods without treatment. Side effects of chemotherapy vary from person to person and also depend on the agents given. Modern chemotherapy agents are usually well tolerated, and side effects for most people are manageable. In general, anticancer medications destroy cells that are rapidly growing and dividing. Therefore, normal red blood cells, platelets, and white blood cells that also are growing rapidly can be affected by chemotherapy. As a result, common side effects include anemia, loss of energy, and a low resistance to infections. Cells in the hair roots and intestines also divide rapidly. Therefore, chemotherapy can cause hair loss, mouth sores, nausea, vomiting, and diarrhea, but these effects are transient.
Treatment of stage IV colorectal cancer
Once colorectal cancer has spread distant from the primary tumor site, it is described as stage IV disease. These distant tumor deposits, shed from the primary tumor, have traveled through the blood or lymphatic system, forming new tumors in other organs. At that point, colorectal cancer is no longer a local problem but is instead a systemic problem with cancer cells both visible on scan and undetectable, but likely present elsewhere throughout the body. As a result, in most cases the best treatment is chemotherapy, which is a systemic therapy. Chemotherapy in metastatic colorectal cancer has been proven to extend life and improve the quality of life. If managed well, the side effects of chemotherapy are typically far less than the side effects of uncontrolled cancer. Chemotherapy alone cannot cure metastatic colon cancer, but it can more than double life expectancy and allow for good quality of life during the time of treatment.
Chemotherapy options for colorectal cancer treatment vary depending on other health issues that an individual faces. For fitter individuals, combinations of several chemotherapeutic drugs usually are recommended, whereas for sicker people, simpler treatments may be best. Different multidrug regimens combine agents with proven activity in colorectal cancer such as 5-fluorouracil (5-FU), which is often given with the drug leucovorin (also called folinic acid) or a similar drug called levoleucovorin, which helps it work better.
Capecitabine (Xeloda), is a chemotherapy drug given in pill form. Once in the body, it is changed to 5-FU when it gets to the tumor site. Other chemotherapy drugs for colorectal cancer are irinotecan (Camptosar), oxaliplatin (Eloxatin), and trifluridine and tipiracil (Lonsurf), a combination drug in pill form. Chemotherapy regimens often have acronyms to simplify their nomenclature (such as FOLFOX, FOLFIRI, and FLOX).
Targeted therapies are newer treatments that target specific aspects of the cancer cell, which may be more important to the tumor than the surrounding tissues, offering potentially effective treatments with fewer side effects than traditional chemotherapy. Bevacizumab (Avastin), cetuximab (Erbitux), panitumumab (Vectibix), ramucirumab (Cyramza), regorafenib (Stivarga), and ziv-aflibercept (Zaltrap) are targeted therapies that have been used in the management of advanced colorectal cancer. These newer chemotherapeutic agents most often are combined with standard chemotherapy to enhance their effectiveness.
If the first treatment is not effective, second- and third-line options are available that can confer benefit to people living with colorectal cancer.
Radiation therapy in the primary treatment of colorectal cancer has been limited to treating cancer of the rectum. As noted earlier, whereas parts of the colon move freely within the abdominal cavity, the rectum is fixed in place within the pelvis. It is in intimate relationship to many other structures and the pelvis is a more confined space. For these reasons, a tumor in the rectum often is harder to remove surgically because the space is smaller and other structures can be involved with cancer. As a result, for all but the earliest rectal cancers, initial chemotherapy and radiation treatments (a local treatment to a defined area) are recommended to try and shrink the cancer, allowing for easier removal and lowering the risk of the cancer returning locally. Radiation therapy is typically given under the guidance of a radiation specialist called a radiation oncologist. Initially, individuals undergo a planning session, a complicated visit as the doctors and technicians determine exactly where to give the radiation and which structures to avoid. Chemotherapy usually is administered daily while the radiation is delivered. Side effects of radiation treatment include fatigue, temporary or permanent pelvic hair loss, and skin irritation in the treated areas.
Radiation therapy will occasionally be used as a palliative treatment to reduce pain from recurrent or metastatic colon or rectal cancer.
- Factors that may increase your risk of colon cancer include:
- Older age. The great majority of people diagnosed with colon cancer are older than 50. Colon cancer can occur in younger people, but it occurs much less frequently.
- African-American race. African-Americans have a greater risk of colon cancer than do people of other races.
- A personal history of colorectal cancer or polyps. If you’ve already had colon cancer or adenomatous polyps, you have a greater risk of colon cancer in the future.
- Inflammatory intestinal conditions. Chronic inflammatory diseases of the colon, such as ulcerative colitis and Crohn’s disease, can increase your risk of colon cancer.
- Inherited syndromes that increase colon cancer risk. Genetic syndromes passed through generations of your family can increase your risk of colon cancer. These syndromes include familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer, which is also known as Lynch syndrome.
- Family history of colon cancer. You’re more likely to develop colon cancer if you have a parent, sibling or child with the disease.
- If more than one family member has colon cancer or rectal cancer, your risk is even greater.
- Low-fiber, high-fat diet. Colon cancer and rectal cancer may be associated with a diet low in fiber and high in fat and calories.
- Research in this area has had mixed results. Some studies have found an increased risk of colon cancer in people who eat diets high in red meat and processed meat.
- A sedentary lifestyle. If you’re inactive, you’re more likely to develop colon cancer. Getting regular physical activity may reduce your risk of colon cancer.
- Diabetes. People with diabetes and insulin resistance have an increased risk of colon cancer.
- Obesity. People who are obese have an increased risk of colon cancer and an increased risk of dying of colon cancer when compared with people considered normal weight.
- Smoking. People who smoke may have an increased risk of colon cancer.
- Alcohol. Heavy use of alcohol increases your risk of colon cancer.
- Radiation therapy for cancer. Radiation therapy directed at the abdomen to treat previous cancers increases the risk of colon and rectal cancer.
- People with an average risk of colon cancer can consider screening beginning at age 50. But people with an increased risk, such as those with a family history of colon cancer, should consider screening sooner.
- Several screening options exist — each with its own benefits and drawbacks. Talk about your options with your doctor, and together you can decide which tests are appropriate for you.
- Make lifestyle changes to reduce your risk
- You can take steps to reduce your risk of colon cancer by making changes in your everyday life. Take steps to:
- Eat a variety of fruits, vegetables and whole grains. Fruits, vegetables and whole grains contain vitamins, minerals, fiber and antioxidants, which may play a role in cancer prevention. Choose a variety of fruits and vegetables so that you get an array of vitamins and nutrients.
- Drink alcohol in moderation, if at all. If you choose to drink alcohol, limit the amount of alcohol you drink to no more than one drink a day for women and two for men.
- Stop smoking. Talk to your doctor about ways to quit that may work for you.
- Exercise most days of the week. Try to get at least 30 minutes of exercise on most days. If you’ve been inactive, start slowly and build up gradually to 30 minutes. Also, talk to your doctor before starting any exercise program.
- Maintain a healthy weight. If you are at a healthy weight, work to maintain your weight by combining a healthy diet with daily exercise. If you need to lose weight, ask your doctor about healthy ways to achieve your goal. Aim to lose weight slowly by increasing the amount of exercise you get and reducing the number of calories you eat.
Colon cancer facts
- Colorectal cancer is a malignant tumor arising from the inner wall of the large intestine (colon) or rectum.
- Colorectal cancer is the third leading cause of cancer in both men and women in the U.S.
- Common risk factors for colorectal cancer include increasing age, African-American race, a family history of colorectal cancer, colon polyps, and long-standing ulcerative colitis.
- Most colorectal cancers develop from polyps. Removal of colon polyps can aid in the prevention of colorectal cancer.
- Colon polyps and early cancer may have no cancer-specific early signs or symptoms. Therefore, regular colorectal cancer screening is important.
- Diagnosis of colorectal cancer can be made by sigmoidoscopy or by colonoscopy with biopsy confirmation of cancerous tissue.
- Treatment of colorectal cancer depends on the location, size, and extent of cancer spread, as well as the health of the patient.
- Surgery is the most common medical treatment for colorectal cancer.
- Early-stage colorectal cancers are typically treatable by surgery alone.
- Chemotherapy can extend life and improve quality of life for those who have had or are living with metastatic colorectal cancer.
- It can also reduce the risk of recurrence in patients found to have high-risk colon cancer findings at surgery.