Colorectal cancer is a form of cancer or malignant tumor that forms in the tissue of the colon and rectum.
The large intestine is part of the body’s digestive system. The digestive system removes and processes nutrients (vitamins, minerals, carbohydrates, fat, protein, and water) from food and helps remove waste material from your body. The digestive system consists of the esophagus, stomach, as well as both small and large intestines. The colon (large intestine) is the first part of the large intestine and is approximately 5 feet long. Together, the rectum and anal canal make up the last section of the large intestine and is about 6-8 inches long. The anal canal ends at the anus (the opening at the end of the large intestine).
Colorectal cancer occurs when tumors form in the lining of the large intestine, in the colon and rectum area. This condition is common in both men and women. The risk of developing colorectal cancer increases after the age of 50. You run a higher risk to develop the disease if you have colorectal polyps, a family history of colorectal cancer, ulcerative colitis or Crohn’s disease, eat a high-fat diet, or are a smoker. Having a parent, brother, sister, or child with colorectal cancer also doubles your risk to develop colorectal cancer.
Symptoms of colorectal cancer include:
- Diarrhea or constipation
- A feeling that your bowel does not empty completely
- Blood (bright red or very dark in color) in your stool
- Smaller or narrower stool than usual
- Frequent pain or cramps, or feeling bloated
- Weight loss for no apparent reason
- Nausea or vomiting
Since you may not have symptoms at first, it is important to undergo a screening test. It is recommended for everyone over the age of 50 to be screened. Tests include colonoscopy and tests to check blood in the stool. Treatments for colorectal cancer include surgery, chemotherapy, radiation, or a combination. If detected early, colorectal cancer can be treated with surgery.
Signs and Symptoms of Colorectal Cancer
- Blood (bright red or very dark in color) in the stool.
- Change in bowel habits
- A feeling that the intestines are not completely empty.
- Stools that are slimmer or have a different shape than normal.
- General stomach discomfort (gas pain, bloating, gas, or cramps).
- Appetite changes.
- Weight loss for no known reason.
- Feeling very tired.
Diagnosis of Colorectal Cancer
It is recommended that people at average risk of colorectal cancer get screened at regular intervals starting from the age of 50. It is recommended that screening should continue until the age of 75; thereafter, the decision to get screening will be based on the patient’s life expectancy, health status, co-morbid conditions, and results of previous screenings.
People who are at high risk due to a family history of colorectal cancer or polyps or because they have inflammatory bowel disease or certain inherited conditions may be advised to start screening before the age of 50 and / or get screened more frequently.
The following methods are considered acceptable screening tests for colorectal cancer:
- High-sensitivity fecal occult blood tests (FOBT). Both polyps and colorectal cancer can bleed, and the FOBT checks for small amounts of blood in the stool that cannot be seen visually. (Blood in the stool can also indicate a non-cancerous condition, such as hemorrhoids.)
Currently, two types of FOBT are approved by the Food and Drug Administration (FDA) for colorectal cancer screening: guaiac FOBT (gFOBT) and faecal immunochemical (or immunohistochemical) test (FIT, also known as iFOBT). With both types of FOBT, a stool sample is collected by the patient using a kit, with the sample returned to the doctor.
- Guaiac FOBT uses chemicals to detect heme, a component of the blood protein hemoglobin. Since guaiac FOBT can also detect heme in some foods (for example, red meat), people should avoid certain foods before taking this test.
- FIT uses antibodies to detect a specific human hemoglobin protein. Dietary restrictions are usually not required for FIT.
Research shows that guaiac FOBT, when taken every 1 to 2 years in people from the age of 50 to 80, can help reduce the number of death cases from colorectal cancer by 15 to 33%. If FOBT is the only type of colorectal cancer screening test available, experts recommend annual testing.
- Stool DNA test (FIT-DNA). The only fecal DNA test approved by the FDA to date, Cologuard®, is a multitarget test that detects small amounts of blood in stool (with an immunochemical test similar to FIT) as well as nine DNA biomarkers in three genes that have been found in colorectal cancer and adenoma advanced pre-cancer rates. DNA comes from cells in the lining of the colon and rectum that are released and collected in the stool as it passes through the colon and rectum. As with both types of FOBT, stool samples for the FIT-DNA test are collected by the patient using the kit; the sample is then tested in the laboratory. The computer program analyzes the results of two tests (blood biomarkers and DNA) and provides negative or positive results. People with a positive test result are advised to undergo a colonoscopy.
When conducting a study on people who were at average risk for developing colon cancer and had no symptoms of colon problems, this test detected more cancers and adenomas than the FIT test (it is more sensitive). However, the FIT-DNA test is more likely to identify gas abnormalities when they are not present (it has a higher number of false positive test results).
- Sigmoidoscopy. In this test, the rectum and sigmoid colon are examined using a sigmoidoscope, a flexible lighted tube with a lens for viewing and a device to remove tissue. This instrument is inserted through the anus into the rectum and sigmoid colon as air (or carbon dioxide) is pumped into the colon to expand it so that doctors can see the lining of the colon more clearly. During a sigmoidoscopy, abnormal growths in the rectum and sigmoid colon can be removed for analysis (biopsy). The lower colon must be clean prior to sigmoidoscopy. However, the preparation is less extensive compared to colonoscopy. In this test, you may not be given sedatives.
Studies have shown that people who undergo routine screening by sigmoidoscopy after the age of 50 have a 60 to 70% lower risk of dying from cancers of the rectum and lower colon than people who do not. A randomized controlled clinical trial found that even just one sigmoidoscopy screening between the age of 55 and 64 could substantially reduce the incidence and mortality of colorectal cancer. Experts generally recommend sigmoidoscopy every 5 years with or without gFOBT or FIT every 3 years for people at average risk of having a negative test result.
- Standard (or optical) colonoscopy. In this test, the rectum and entire colon are examined using a colonoscopy – a flexible lighted tube with a lens for viewing and a device to remove tissue. Resembling a shorter sigmoidoscope, the colonoscope is inserted through the anus into the rectum and colon as air (or carbon dioxide) is pumped into the colon to expand it so that the doctor can see the lining of the colon more clearly. During a colonoscopy, any abnormal growths in the colon and rectum can be removed, including growths in the upper part of the large intestine that are beyond the reach of sigmoidoscopy. Prior to this test, a thorough cleaning of the entire colon is required. Most patients would be given sedatives during the test.
Studies show that colonoscopy reduces death from colorectal cancer by about 60 to 70%. Additional studies are still being conducted to further evaluate the effectiveness of the colonoscopic screening method. Experts recommend a colonoscopy every 10 years for people at average risk – as long as their test result is negative.
- Virtual colonoscopy. This screening method, also called computed tomographic colonography (CT), uses special x-ray equipment (CT scanner) to produce a series of images of the colon and rectum from outside the body. The computer then collects these images into detailed images that can show polyps and other abnormalities. Virtual colonoscopy is less invasive than standard colonoscopy and does not require sedatives. As with standard colonoscopy, a thorough cleaning of the colon is required prior to this test, and air (or carbon dioxide) is pumped into the colon to expand it to better view the lining of the intestine. The accuracy of virtual colonoscopy is similar to standard colonoscopy, and virtual colonoscopy has a lower risk of complications. However, if polyps or other abnormal growths are found during virtual colonoscopy, a standard colonoscopy is usually performed to remove them.
It is not clear whether virtual colonoscopy can help reduce deaths from colorectal cancer. Researchers are still trying to compare virtual colonoscopy with other screening methods.
- Other methods. There are several other tests for colorectal cancer screening — although these tests are generally not recommended.
Double contrast barium enema. This test, also called a DCBE (double-contrast barium enema), is another method of visualizing the colon from outside the body. With DCBE, a series of x-ray images of the entire colon and rectum are taken after the patient is enemaed with a barium solution. The barium helps outline the colon and rectum in the image. DCBE is rarely used for screening as it is less sensitive than colonoscopy in detecting small polyps and cancer. However, it can be used for people who are unable to undergo a standard colonoscopy since they run higher risk to have complications.
Single-specimen guaiac FOBT. Doctors sometimes run single-specimen guaiac FOBT on a stool (stool) sample taken during a digital rectal exam as part of a routine physical exam. However, this approach has not been shown to be an effective means of screening for colorectal cancer.
Prognosis of Colorectal Cancer
Prognosis (chances of recovery) and treatment options depend on the following:
- Stage of cancer (whether the cancer is in the inner lining of the colon only or has spread to the intestinal wall, or has spread to lymph nodes or elsewhere in the body).
- Whether the cancer has blocked or made a hole in the colon.
- Whether any cancer cells still remain after surgery.
- Whether the cancer has recurred.
- The patient’s general health.
Prognosis also depends on the level of carcinoembryonic antigen (CEA) in the blood before treatment is started. CEA is a substance in the blood that may increase when cancer is present.
Stages Of Colorectal Cancer
After colon cancer is diagnosed, certain tests will be performed to identify if cancer cells have spread within the colon or to other parts of the body – this process is called staging. Staging determines levels of severity for disease as well as the treatment option.
The following tests and procedures can be used in the staging process:
- CT scan (CAT scan): A procedure that produces a series of detailed images of an area in the body, such as the stomach or chest – taken from various angles. The images are created by a computer connected to an x-ray machine. The dye can be injected into a vein or swallowed to help an organ or tissue appear more clearly. This procedure is also called computed tomography, computerized tomography, or computerized axial tomography.
- MRI (magnetic resonance imaging): A procedure that uses magnets, radio waves, and a computer to create a series of detailed images of areas inside the colon. A substance called gadolinium is injected into the patient through a vein. Gadolinium collects around the cancer cells to provide a brighter image. This procedure is also called nuclear magnetic resonance imaging (NMRI).
- PET scan (positron emission tomography scan): A procedure to find malignant tumor cells in the body. A small amount of radioactive glucose (sugar) is injected into a vein. The PET scanner rotates around the body and creates images of where glucose is being used in the body. Malignant tumor cells appear lighter in the image because they are more active and take up more glucose than normal cells.
- Chest x-ray: X-ray of the organs and bones inside the chest. An x-ray is a type of energy beam that passes through the body and onto film – creating images of areas inside the body.
- Surgery: A procedure to remove a tumor and see how far it has spread in the large intestine (colon).
- Lymph node biopsy: The removal of complete or partial of a lymph node. The pathologist views the tissue under a microscope to look for cancer cells.
- Complete Blood Count (CBC): A procedure in which a blood sample is drawn and checked for the following:
- The number of red blood cells, white blood cells, and platelets.
- The amount of hemoglobin (a protein that carries oxygen) in red blood cells.
- The portion of the blood sample made up of red blood cells.
- Carcinoembryonic Antigen Test (CEA): A test that measures the level of CEA in the blood. CEA is released into the bloodstream from cancer cells and normal cells. If it is found to be higher than normal, it can be a sign of colon cancer or other conditions
There are three ways cancer spreads in the body.
Cancer can spread through the tissues, lymph system, and blood:
- Tissues. Cancer spreads from where it started by growing to nearby areas.
- Lymph system. Cancer spreads from where it started by getting into the lymph system. Cancer spreads through lymph vessels to other parts of the body.
- Blood. Cancer spreads from where it started by entering the blood. Cancer spreads through the blood vessels to other parts of the body.
Cancer can spread from the part of the body where it started to other parts of the body
When cancer spreads to other parts of the body, it is called metastasis. Cancer cells break away from where they started (the main tumor) and travel through the lymph or blood system.
- Lymph system. Cancer gets into the lymph system, spreads through the lymph vessels, and forms tumors (metastatic tumors) in other parts of the body.
- Blood. Cancer enters the blood, spreads through the blood vessels, and forms tumors (metastatic tumors) in other parts of the body.
Metastatic tumors are the same type of cancer as primary tumors. For example, if colon cancer spreads to the lungs, the cancer cells in the lungs are actually colon cancer cells. This disease is metastatic colon cancer, not lung cancer.
Treatment for Colorectal Cancer
A variety of treatments are available to treat colorectal cancer. Some are standard treatments, and some are still in clinical trials. A clinical trial is research intended to help improve current treatments or gather information about new treatments for cancer patients. When clinical trials show that the new treatment is better than standard treatment, the new treatment can become the standard treatment. Certain clinical trials are only open to patients who have not undergone any treatment.
Six types of standard treatment are used:
Surgical removal of cancer is the most common treatment for all stages of colon cancer. One of the following types of surgery can be done to remove cancer:
- Local excision: If cancer is found at a very early stage, the surgeon can remove it without cutting the abdominal wall. Instead, the surgeon may put a tube with a cutting device through the rectum into the colon and cut the cancer. This is called local excision. If cancer is found in a polyp (a small, raised area of tissue), this surgery is called a polypectomy.
- Colon resection with an anastomosis: If the cancer is larger, the surgeon will perform a partial colectomy (removing the cancer and a small amount of healthy tissue nearby). Then, the surgeon can perform anastomosis (the healthy part of the large intestine are stitched together). Usually, the surgeon will also remove lymph nodes near the colon and examine them under a microscope to see if they contain cancer.
- Colon resection with a colostomy: If the doctor is unable to suture the two ends of the colon back together, a stoma (opening) is made outside of your body so that the stool can pass through. This procedure is called a colostomy. A bag is placed around the stoma to collect stool. In some cases, a colostomy is only allowed after the lower colon has recovered. However, if the surgeon needs to remove the entire lower colon – the colostomy may be permanent.
Even if the doctor removes all the visible cancer, some patients may be given chemotherapy or radiation therapy after surgery to kill any remaining cancer cells. Treatment given to patients after primary surgery helps reduce the risk of recurrence – this is called adjuvant therapy.
Radiofrequency ablation is the use of special probes with tiny electrodes that kill cancer cells.In some procedures, the probe is inserted directly through the skin and local anesthesia is required. In other cases, a probe is inserted through an incision in the abdomen. The patient will be under general anesthesia.
Cryosurgery is a treatment that uses instruments to freeze and destroy abnormal tissue. This type of treatment is also called cryotherapy.
Chemotherapy uses drugs to stop the growth of cancer cells, either by killing the cells or by stopping them from dividing. Either through oral or injection chemotherapy, the drugs enter the bloodstream and reach cancer cells throughout the body (systemic chemotherapy). Chemotherapy can be placed directly into the cerebrospinal fluid, organs, or body cavities (e.g: the stomach), or affect cancer cells in the areas concerned (regional chemotherapy).
Chemoembolization of the hepatic artery can be used to treat cancer that has spread to the liver. This involves blocking the hepatic artery (the main artery that supplies blood to the liver) and injecting an anticancer drug between the blockage and the liver. The liver arteries then deliver drugs throughout the liver. Only a small amount of the drug reaches other parts of the body. The blockage may be temporary or permanent – depending on what is used to block the artery. The liver continues to receive some blood from the hepatic portal vein – which carries blood from the stomach and intestines.
Chemotherapy will depend on the type and stage of cancer.
Radiation therapy is a cancer treatment that uses high-energy X-rays or other types of radiation to kill cancer cells or stop them from growing. There are two types of radiation therapy:
- External radiation therapy uses a machine outside the body to send radiation towards the cancer.
- Internal radiation therapy uses a radioactive substance sealed in a needle, granule, cable, or catheter that is placed directly into or near the cancer site.
Radiation therapy will be given depending on the type and stage of cancer. External radiation therapy is used as palliative therapy to relieve symptoms and improve quality of life.
Targeted therapy is a type of treatment that uses drugs or other substances to identify and attack specific cancer cells without damaging normal cells.
Types of targeted therapy used in the treatment of bowel cancer include the following:
- Monoclonal antibody: Monoclonal antibody is made in the laboratory from one type of immune system cell. These antibodies can identify substances in cancer cells or normal substances that can help cancer cells grow. Antibodies attach to the substance and kill cancer cells, block their growth, or prevent them from spreading. Monoclonal antibodies are given through intravenous infusion. Antibodies can be used independently or are delivered directly to the cancer cells through medications, toxins, or radioactive materials.
- Bevacizumab and ramucirumab are types of monoclonal antibodies targeting a protein called vascular endothelial growth factor (VEGF). This can prevent the growth of new blood vessels that the tumor needs to grow.
- Cetuximab and panitumumab are types of monoclonal antibodies targeting a protein called epidermal growth factor receptor (EGFR) on the surface of certain types of cancer cells. This can stop cancer cells from growing and dividing.
- Angiogenesis inhibitors: Angiogenesis inhibitors block new blood vessels that support tumor growth:
- Ziv-aflibercept is a vascular endothelial growth factor trap that blocks an enzyme needed for the growth of new blood vessels in tumors.
- Regorafenib is used to treat colorectal cancer that has spread to other parts of the body and has not improved with other treatments. It blocks the action of certain proteins, including vascular endothelial growth factors. This can help prevent cancer cells from growing and can kill cancer cells. It can also block the new blood vessels that support tumor growth.
Risk Factors of Colorectal Cancer
The following risk factors increase the risk of colorectal cancer:
The risk of colorectal cancer increases after a person passes the age of 50. Most cases of colorectal cancer are diagnosed after the age of 50.
Family history of colorectal cancer
Having a parent, sibling, or a child with colorectal cancer doubles a person’s risk of developing colorectal cancer.
- Previous colorectal cancer.
- High-risk adenoma (colorectal polyps 1 centimeter or larger / have abnormal cells when viewed under a microscope).
- Ovarian cancer
- Inflammatory bowel disease (such as ulcerative colitis or Crohn’s disease).
The risk of colorectal cancer increases when certain gene changes associated with familial adenomatous polyposis (FAP) or hereditary nonpolyposis colon cancer (HNPCC or Lynch syndrome) are inherited.
Having three or more alcoholic drinks per day increases the risk of colorectal cancer. Drinking alcohol is also linked to the risk of developing large colorectal adenomas (benign tumors).
Secondhand smoke is associated with an increased death risk of colorectal cancer. In addition, it is also associated with an increased risk of developing colorectal adenomas. Active smokers who have had surgery to remove a colorectal adenoma are at increased risk for adenoma recurrence.
Obesity is also associated with an increased death risk of colorectal cancer.
Prevention of Colorectal Cancer
Avoiding the risk factors and increasing the protective factors can help reduce one’s chances of getting colon cancer.
The following are some protective factors that can decrease your chance of getting colorectal cancer:
A healthy lifestyle with regular physical activity is associated with a reduced risk of colorectal cancer.
Research has shown that taking aspirin lowers the death risk of colorectal cancer. The effect may begin to be seen 10 to 20 years after the patient starts taking aspirin.
Possible dangerous side effects of daily aspirin consumption (100 mg or less) include an increased risk of stroke and gastrointestinal bleeding.
Combination hormone replacement therapy
Research shows that hormone replacement therapy (HRT), which combines estrogen and progestin – lowers the risk of invasive colorectal cancer among postmenopausal women.
However, if you take combined HRT and develop colorectal cancer – the cancer will be more likely to progress and you still run the risk of dying from colorectal cancer.
Possible dangers of HRT lead to an increased risk of experiencing:
- Breast cancer.
- Heart disease.
- Blood clots.
Most colorectal polyps are adenomas – which can develop into cancer. Removing colorectal polyps that are larger than 1 centimeter (the size of a pea) can lower the risk of colorectal cancer. It is unclear as to whether the removal of smaller polyps decreases the chance of getting colorectal cancer.
Possible complications of polyp removal include sigmoidoscopy bleeding from the polypectomy site and perforation (a hole or tear) of the colon.