Colorectal Cancer – Causes, Signs and symptoms

Colorectal cancer

Reviewed By:
Mark Oren, M.D., FACP


Colorectal cancer refers to the uncontrolled growth of abnormal cells in the colon or rectum, which are part of the digestive system. This cancer usually begins as polyps, which are abnormal growths in the inner lining of the colon or rectum. Polyps are not cancer but can become cancerous over the years. More than 95 percent of colorectal cancer is adenocarcinoma, which is cancer of the gland cells that line the inside wall of the large intestine.

Some risk factors for colorectal cancer cannot be controlled, such as having a family history of this cancer, age and ethnicity. A person with a history of chronic inflammatory bowel disease also has a higher risk for developing colorectal cancer.

However, some lifestyle habits can increase the risk of this cancer. A diet high in animal fat and low in fiber, physical inactivity and smoking are some of the lifestyle habits that increase the risk for colorectal cancer.

Screening for colorectal cancer is important because symptoms of the disease may be absent or may be related to other conditions. Possible indicators include changes in bowel habits, abdominal pain and bleeding from the rectum.

Diagnostic tests for colorectal cancer include tests for blood in the stool, a special type of enema x-ray, flexible sigmoidoscopy and colonoscopy. Ultrasound, blood tests, x-rays and magnetic resonance imaging (MRI) also may be used to help diagnose the condition. 

The most common treatment for colorectal cancer is surgery. Patients may also receive radiation therapy or chemotherapy before or after surgery, or instead of surgery if surgery is not feasible. In many cases, patients may receive a combination of these therapies. A patient’s cancer care team, which is typically headed by a medical oncologist, is responsible for the planning and implementation of the treatment plan.

The American Cancer Society (ACS) estimates that in 2007 there will be more than 112,000 new cases of colon cancer and nearly 42,000 of rectal cancer in the United States. Together, these cancers will cause about 53,000 deaths in 2007.

Colorectal cancer is the number two cause of cancer-related deaths in the United States, surpassed only by lung cancer. However, the mortality rate from this disease has declined over the past 15 years. This decrease may be attributed to a higher number of polyps being found by screenings when they are precancerous. Also, colorectal cancer is being detected and treated in earlier stages when the disease is more likely to be cured. The ACS estimates that there are more than 1 million colorectal cancer survivors in the United States today.

About colorectal cancer

Colorectal cancer involves uncontrolled growth of abnormal cells in the colon or rectum. It is the third most common form of cancer in the United States. Colorectal cancer is the third leading cause of cancer deaths for both men and women, but when the deaths by gender are combined, it is the second leading cause of cancer deaths overall. Among men, colon cancer is surpassed by lung cancer and prostate cancer. In women, it is third behind lung and breast cancer in occurrence and mortality. However, the mortality rate has declined for the past 15 years, which is most likely due to improved screening and treatment methods.

The colon and rectum are part of the gastrointestinal system. The first 6 feet (1.8 meters) of the large intestine comprise the colon. The last 6 inches (15 centimeters) is the rectum, which ends at the anus. Although the large intestine includes the colon and rectum, the term colon is often used as a synonym for large intestine or large bowel.

The colorectal tract is a muscular tube at the lower end of the digestive system. It is shaped somewhat like a question mark. The colon consists of the:

  • Ascending colon. Starts at the end of the small intestine and goes upward on the right side of the abdomen.

  • Transverse colon. Continues across the body from the right to left side.

  • Descending colon. Extends downward on the left side.

  • Sigmoid colon. A small S-shaped section that connects to the rectum.

The small intestine absorbs most nutrients before digested food moves to the colon. The colon absorbs water and minerals and stores the rest as waste before expelling the waste through the rectum as feces, or stool.

The colon and rectum consist of several layers of tissue. Colorectal cancer starts in the inner lining, usually as abnormal growths called polyps. Polyps may remain benign, but some are precancerous and over the years turn malignant. The polyps most likely to advance to cancer are adenomatous polyps, or adenomas. The adenomatous cells are gland cells on the inner lining of the colorectal tract. Other types of polyps include inflammatory polyps, which are not precancerous, and hyperplastic polyps, which can be precancerous.

According to the National Cancer Institute (NCI), polyps are a cause for concern because:

  • Precancerous polyps occur in about 40 percent of people over age 50.

  • About 5 to 10 percent of polyps become cancer if not removed.

  • Physicians cannot determine which polyps will lead to cancer.

  • People who have had a polyp have up to a 50 percent increased risk of developing more polyps within three years.

Colorectal cancer can spread from the innermost mucosal layer to the wall of the colorectal tract and beyond. Cancer in the colorectal wall can grow into the blood vessels or lymph vessels. These vessels can allow metastasis (spread) of the cancer to distant parts of the body. Prognosis (outlook) is best when cancer is confined to the innermost layer and does not block or perforate the large intestine.

Unlike some forms of cancer, early detection of colorectal cancer is possible through screening tests (see Diagnosis methods). However, most Americans do not follow the recommended schedule of tests, according to the Centers for Disease Control and Prevention (CDC). A major reason is embarrassment with the type of tests and reluctance to undergo certain procedures. However, increased screening could further reduce the incidence and death rate of colorectal cancer.

The importance of screening is apparent in the survival rates for colorectal cancer. Ninety percent of people treated for early-stage (non-metastatic) colorectal cancer survive at least five years and often much longer, according to the American Cancer Society (ACS). However, only 39 percent of colorectal cancer is detected early. For later stages of colorectal cancer, the five-year survival rate declines to:

  • 68 percent when colorectal cancer spreads to nearby organs or lymph nodes

  • 10 percent when colorectal cancer spreads to distant organs or lymph nodes

The ACS predicts there will be about 112,000 new cases of colon cancer and nearly 42,000 new cases of rectal cancer in the United States in 2007. Colorectal cancer causes about 10 percent of all cancer deaths in the United States and is expected to kill more than 53,000 Americans in 2007. There are about 1 million Americans who have survived colorectal cancer.

Types and differences of colorectal cancer

More than 95 percent of colorectal cancers are adenocarcinoma, which is cancer of the gland cells that line the inside wall of the colon and rectum. These usually develop from adenomatous polyps (also called adenomas), abnormal precancerous growths that can form in the inner lining of the colon and rectum. Some adenomatous polyps and other kinds of polyps, such as inflammatory polyps, remain benign.

Uncommon types of colorectal cancer include:

  • Carcinoid tumor. Develops from the colon’s hormone-producing cells.
  • Gastrointestinal stromal tumor (GIST). Develops in the colon wall from specialized cells called interstitial cells of Cajal.
  • Lymphoma. Cancers of the immune system that usually start in lymph nodes.

Risk factors and causes of colorectal cancer

Scientists are not certain how colorectal cancer begins but some controllable and uncontrollable risk factors have been associated with the disease. The risk of colorectal cancer rises with age. More than 90 percent of cases affect people age 50 and older. Other factors that increase the chance of developing colorectal cancer:

  • Personal medical history of colon, rectal, ovarian, endometrial or breastcancers.

  • Family history of colorectal cancer. Individuals who have two or more close relatives with colorectal cancer account for about 20 percent of patients with colorectal cancer, according to the American Cancer Society (ACS).

  • Colon polyps.

  • Chronic inflammatory bowel diseases. These include ulcerative colitis, or ulcers in the lining of the colon, and Crohn’s disease, an inflammation of the gastrointestinal tract.

  • Diabetes.  Recent studies have found a correlation between this metabolic disorder and colorectal malignancy. Individuals with diabetes have a 30 to 40 percent increased risk of colorectal cancer, according to the ACS. Researchers suspect that certain lifestyle habits (e.g., diet) may be associated with both diabetes and colorectal cancer.

  • Hereditary colorectal disorders. Inherited gene mutations account for 5 to 10 percent of people with colorectal cancer.  Genetic tests can detect these defects in DNA. The ACS recommends that people with a family history of colorectal cancer ask their physician about genetic counseling and testing. Inherited colorectal disorders that can be detected with genetic testing include:

    • Familial adenomatous polyposis (FAP). A condition in which hundreds of polyps develop. This usually develops between age 5 and 40. Most people with FAP will develop colorectal cancer by age 40 unless they have their colon removed.

    • Hereditary nonpolyposis colon cancer  (HNPCC). Also know as Lynch syndrome, this condition occurs at a young age causing few rather than hundreds of polyps. Individuals with this condition have an 80 percent chance of developing colon cancer by age 75. HNPCC also increases the risk of other cancers, including stomach, pancreas and endometrial cancer in women.

    • Peutz-Jeghers syndrome (PJS).This condition can cause the development of numerous polyps in the small intestine and colon. People who have been diagnosed with PJS have a 39 percent risk of developing colon cancer by age 64.

    • Juvenile polyposis. A genetic condition that causes polyps to grow throughout the intestinal tract beginning in early childhood. These individuals have a greater risk of developing colon cancer by age 60.
  • Ethnicity. Jews of Eastern European descent (Ashkenazi Jews) appear to have more colorectal cancer, perhaps due to an identified genetic mutation.

  • Night-shift work.  People who work consistently at night may have a higher risk of colorectal cancer. One study found a higher incidence of the disease in individuals who worked a night shift at least 3 nights a month for 15 months or more. Scientists suspect the greater risk may be related to melatonin levels in the body that may change according to light exposure. Additional research is necessary to confirm the association with colorectal cancer.

The Centers for Disease Control and Prevention (CDC) lists the following as lifestyle risk factors for colorectal cancer. Individuals can change these lifestyle habits to reduce their risks:

  • Lack of regular physical activity
  • Diet high in fat, particularly from animal sources
  • Diet low in fiber, vegetables and fruits
  • Obesity
  • Heavy consumption of alcohol
  • Use of tobacco

Signs and symptoms of colorectal cancer

In some cases, colorectal cancer has no symptoms. The possible indicators of colorectal cancer may be due to other conditions as well. Individuals should consult a physician if the following symptoms appear:

  • A change in bowel habits, including stools that are narrower than usual
  • Blood (bright red or dark) in the stool or in the toilet after a bowel movement
  • Bleeding from the rectum
  • Diarrhea
  • Constipation or a feeling that the bowel has not emptied
  • An urge to have a bowel movement when there is no need
  • Abdominal discomfort including cramps, gas pains, bloating or fullness
  • Unexplained weight loss
  • Fatigue
  • Vomiting

Diagnosis methods for colorectal cancer

Unlike many kinds of cancer, colorectal cancer can be found in early stages. Early diagnosis usually results in better chances for curing the disease. Screening tests for colorectal cancer include:

  • Fecal occult blood test (FOBT). This test checks for blood in stool samples. Patients receive a kit that can be completed in a doctor’s office or with instructions to be completed at home. Dietary restrictions may include avoiding red meat, vitamin C, aspirin and aspirin substitutes for several days before testing. Patients return the kit to their physician’s office or a medical lab for analysis. Some home kits provide immediate results through the use of chemically treated papers. These strips of paper can detect the presence of occult blood. Typically, three bowel movements are tested and the results are recorded by the patient. The results are then mailed back to the physician’s office.

    Annual FOBT can reduce deaths from colorectal cancer by 33 percent and incidence of colorectal cancer by 20 percent, according to the U.S.  Centers for Disease Control and Prevention (CDC). Colorectal cancer does not always cause bleeding, and this test can therefore give false negatives (indicating no cancer when cancer is present).
  • Fecal immunochemical test (FIT). This test works similar to the FOBT but is a more specific assessment of a blood protein, which can reduce the number of false negatives. It is easier to use because it does not involve dietary restrictions and usually requires two stool samples rather than three. However, like FOBT it does not reveal tumors that do not bleed.
  • Flexible sigmoidoscopy. The physician inspects the interior of the rectum and the lower colon (the sigmoid) with a flexible, lighted tube called a sigmoidoscope. Deaths from cancer of the rectum and sigmoid colon are more than 50 percent lower among people who have had sigmoidoscopy, according to the CDC.
  • Colonoscopy. A longer flexible, lighted tube with a camera lens called a colonoscope that allows a physician to inspect the rectum and entire colon. The device is connected to a video camera and monitor. The physician may pass a wire through the colonoscope to remove polyps with an electric current. Tissue samples can be taken for microscopic examination in a biopsy.
  • Double-contrast barium enema. X-rays are taken after a chemical compound containing barium is administered into the patient’s rectum through a tube. Air is also pumped into the rectum to enlarge the bowel. The barium outlines the colon and rectum on the x-ray image and helps reveal abnormalities, such as polyps. 

A newer procedure that might be an option is virtual colonoscopy (colonography or CT colonography). This test uses a CAT scan to take pictures of the colon. A CAT scan creates cross-sectional images than can reveal polyps or other irregularities. However, virtual colonoscopy is not as accurate as colonoscopy and is not as widely available. The ACS does not recommend it for early diagnosis of colorectal cancer until more research confirms its effectiveness.

In some men, a digital rectal exam (DRE) is part of a physical examination. The physician carefully inserts a gloved, lubricated finger several inches into the rectum to feel for abnormalities. However, the CDC and ACS advise against screening for colorectal cancer with only the DRE because it involves only a small part of the colorectal tract.

Other tests that may be used in diagnosing or treating colorectal cancer:

  • Blood tests. Includes complete blood count and tumor marker tests (substances tumors release into the blood).
  • Ultrasound. Use of harmless sound waves that create echoes to form a picture of the colon or rectum.
  • Magnetic resonance imaging (MRI).  Use of radio waves and a magnetic field to create a picture of the colon or rectum.
  • Computed tomography (CT or CAT scan). A type of x-ray that produces cross-sectional images of the body. A contrast dye may be injected into a patient’s vein to help highlight the inner structures. A type of CAT scan that may be used with metastatic colorectal cancer is spiral CT, in which the injected dye travels to the liver to reveal if cancer has spread to this organ.
  • Angiography. A type of x-ray that reveals abnormalities in blood vessels. A contrast dye is injected into a vein or an artery. This test may be used to help surgeons identify blood vessels feeding a cancer that has spread to the liver. The test can help with surgical treatment of the cancer.
  • Positron emission tomography (PET). Use of a radiation-detecting PET machine to scan the entire body for cancer. A small amount of a radioactive sugar substance is injected into the patient before a series of images are taken. Cancer cells absorb large amounts of this radioactivity and show up on the scan as “hot spots.” A PET scan is often used to help determine if and where cancer has spread in the body. Technology that combines PET and CT scanning is also being used for more accurate staging and treatment of colorectal cancer.

The ACS recommends that both men and women at average risk should complete ONE of the following screening options:

  • FOBT (or FIT) every year
  • Flexible sigmoidoscopy every five years
  • Blood stool test every year plus flexible sigmoidoscopy every five years
  • Double barium contrast enema every five years
  • Colonoscopy every 10 years

People at higher risk of colorectal cancers should start screening at a younger age and may need testing more often, according to the CDC. The American Cancer Society (ACS) recommends that people with familial adenomatouspolyposis begin colonoscopy during their teens.

Treatment options for colorectal cancer

Possible approaches to treating colorectal cancer depend largely on the stage of the disease and the patient’s age and general state of health. There are three standard treatments: surgery, radiation therapy and chemotherapy.

Surgical removal of the cancer is the most common treatment for colorectal cancer. A surgeon may perform one of the following procedures:

  • Local excision. Removal of early-stage cancer without cutting into the abdomen. This can involve polypectomy, removal of a polyp during a colonoscopy. Local excision also may be performed through the anus if the lesions are small and close to the anus.

  • Colectomy (also called resection). Removal of a larger cancer and a small amount of healthy tissue around it. The surgeon then performs anastomosis, which involves sewing the healthy parts of colon or rectum together, sewing the remaining colon to the rectum or sewing the remaining rectum to the anus.

    In some cases, laparoscopic surgery may be performed to remove colon cancer. This procedure involves only a few small incisions in the in the abdomen instead of a larger one. The surgery is completed using a lighted tube and special instruments inside the body. The recovery time is usually faster for laparoscopic procedures than traditional surgery. Some studies have shown that laparoscopic surgery may produce better long-term results than traditional surgery.
  • Colectomy and colostomy. Creation of an opening (stoma) through the lower abdomen to allow waste to exit the body. Colostomy is completed if anastomosis is not possible. In some cases, colostomy is temporary and reversed after the lower colon heals. Colostomy may be permanent if the entire lower colon is removed.

  • Radiofrequency ablation. Use of a probe that has cancer-killing electrodes. Local anesthesia is used if the probe can be inserted through the skin. General anesthesia is used in a hospital if the probe must be inserted through an incision in the abdomen.

  • Cryotherapy (cryosurgery). Use of an instrument that freezes and destroys abnormal growths. Ablation and cryotherapy are not generally useful for the primary tumor.

Radiation therapy may be used to treat the disease, either before or after surgery. This treatment uses precise high energy x-rays to kill or shrink cancer cells.  It may be performed to reduce large tumors before surgery or to kill any cancer cells left after surgery. In advanced cases of colorectal cancer, radiation may be used to reduce pain, intestinal blockage or other symptoms. Side effects of radiation used on colorectal cancer are often temporary. They include sexual problems, diarrhea, nausea and fatigue. Types of radiation include:

  • External beam radiation therapy. Radiation is emitted by a machine outside the body to destroy cancer cells in a targeted, focused area.

  • Endocavitary radiation therapy. This is similar to external beam but has the advantage of being aimed through the anus to the rectum, thus avoiding the abdominal tissues.

  • Brachytherapy (internal radiation therapy). Small radioactive pellets are placed into or next to the cancer. This may be used in people with rectal cancer who cannot tolerate surgery.

Chemotherapy is the use of powerful drugs to kill or control cancer cells. It may be used for the same reasons as radiation therapy, including reducing cancer before surgery or destroying cancer cells that remain after surgery. In addition, chemotherapy is used to treat the entire body when cancer has spread to tissues and organs. Chemotherapy may be combined with radiation therapy in treatment. It may also be used as adjuvant or prophylactic therapy when there is no evidence of cancer but there is a risk of recurrence.

Researchers are testing other approaches for colorectal cancer treatment in clinical trials not available to the general patient population. This includes biological therapy, which uses the patient’s immune system to fight cancer as well as certain methods that directly attack the cancer.  New drugs are also being used that target human growth factors. Growth factors are substances in the body that help tumors grow. Certain drugs are being tested in clinical trials that can spot these factors and neutralize them, thereby helping prevent cancer cells from growing and spreading. Another drug (bevacizumab) that interferes with the formation of blood vessels that nourish a tumor has also been approved to treat colorectal cancer.

Prevention methods for colorectal cancer

There is no single way to prevent colorectal cancer but people can reduce their odds of developing the disease. Regular testing according to established screening guidelines is the single best way to detect conditions that can lead to colorectal cancer. Individuals can also make healthful changes in their life including:

  • Eating more fiber, vegetables, fruits and whole grains
  • Eating less red meat and other sources of animal fats
  • Exercising at least 30 minutes five days a week
  • Not smoking
  • Limiting consumption of alcohol

Scientists believe that risk of colorectal cancer may be reduced through the use of aspirin, ibuprofen and other nonsteroidal anti-inflammatory drugs. Hormone replacement therapy also may decrease the risk of colorectal cancer. In addition, some studies have shown that high doses of vitamin D taken daily may reduce the risk of the disease. However, these treatments carry other risks and may not be appropriate for all individuals. A physician should be consulted regarding the potential benefits and risks of any treatment or prevention method.

Ongoing research regarding colorectal cancer

Scientists are undertaking much research about colorectal cancer, including clinical trials of medications and other treatments that may improve the detection and treatment of the disease. Areas of focus include:

  • Tumor growth factors. Growth factors are hormone-like substances in the body that encourage growth of cells. Researchers have identified several growth factors associated with colorectal cancer and are developing drugs to control these growth factors. New drugs that interfere with the formation of blood vessels, which supply nutrition to tumors, are also being studied in clinical trials.
  • Chemoprevention. Use of natural or synthetic chemicals to reduce a person’s risk of cancer. Scientists are studying whether fiber, minerals and vitamins and can help prevent colorectal cancer. Research also focuses on the development of new drugs for chemoprevention.
  • Genetics. Researchers are learning more about gene mutations and hereditary conditions associated with colorectal cancers. They are trying to develop tests of stool samples that reveal genetic risk factors and to develop genetic treatments.
  • Immunotherapy. Use of the patient’s immune system to attack colorectal cancer. Vaccines and injections to bolster immune reactions are being studied.
  • Diet and nutrition. Researchers continue to examine the association of diet with colorectal cancer. Certain foods, particularly red meat, appear to increase the risk of colorectal cancer, while fiber may lower the risk. Other elements, such as calcium,  folic acid and large amounts of vitamin D may help reduce the risk of the disease. Studies continue to evaluate the role of these elements in the cause and prevention of thee disease.

Staging of colorectal cancer

The most common way of staging (describing the severity) of colorectal cancer is the American Joint Committee on Cancer’s TNM system. It includes information about the tumor, any involvement of lymph nodes and any metastasis (spread to other parts of the body). The stages for colorectal cancer are:

  • Stage 0 (also called carcinoma in situ). Cancer is found in the innermost lining of the colon and/or rectum only.
  • Stage I. Cancer has spread beyond the innermost lining of the colon and/or rectum to the second and third layers and involves the inside wall of the colon and/or rectum, but it has not spread to the outer wall or outside the colon and/or rectum.
  • Stage II. Cancer has spread outside the colon and/or rectum to nearby tissue, but it has not gone into the lymph nodes.
  • Stage III. Tumor cells have spread to lymph nodes near the colon/rectum.
  • Stage IV colorectal cancer. Cancer may have spread to nearby lymph nodes and has spread to other parts of the body, such as the liver or lungs.

In addition there is recurrent colorectal cancer, when the disease returns after treatment. It may be treated with a combination of surgery, radiation therapy or chemotherapy.

Survival rates vary greatly depending on the stage in which colorectal cancer is diagnosed and treated. Cancer that is detected in the early stages before it has spread in the body has a better survival rate. According to the American Cancer Society, the five-year survival rate for colorectal cancer by stage is as follows:

StageFive-year Survival Rate
Stage I93 percent
Stage II72 to 85 percent
Stage III44 to 83 percent
Stage IV8 percent

Questions for your doctor

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about colorectal cancer:

  1. Am I at a higher risk for this type of cancer?
  2. What are the best screening tests for me?
  3. How often should I have the tests?
  4. What happens if you find a polyp during my colonoscopy?
  5. What is the next step if the polyp is cancerous?
  6. What type of colorectal cancer do I have?
  7. What is the prognosis for my type and stage of cancer?
  8. What are my treatment options?
  9. What can I expect as side effects from the treatment?
  10. If I need a colostomy, will it be permanent?
  11. What are the chances of a recurrence of my cancer if it is removed?
  12. Are there any changes in my lifestyle that can reduce the risk of colorectal cancer?
  13. Does my colorectal cancer place me at risk for other cancers?
  14. Are my children at higher risk for colorectal cancer?
  15. Should I consider genetic testing for colorectal cancer?
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