Colorectal cancer or colon cancer is cancer that affects the colon or rectum due to the development of tumors along the lining of the large intestine. The tumors that develop are usually benign, often taking shape of a polyp (a cluster of small cells) which can become cancerous overtime. These tumors have the ability to spread to various parts of the body. Once the cancer cells begin to spread, the cancer is very hard to control, resulting in a much higher fatality.
Colon cancer is the fourth most common cancer found in both men and women, despite the decline in overall diagnosis and an increase in the screening process. Many people who are at high risk for the disease often do not get screened, resulting in a higher death rate overall.
Colon cancer can affect both men and women, with men being at a higher risk. Risk factors to colon cancer include: obesity, sex, race, and genetics. Age also plays a factor in the development of colon cancer, with 90% of cases being in individuals over 50 years old. Those who have been diagnosed with Crohn’s disease or ulcerative colitis are also at a higher risk of developing colon/colorectal cancer due to the colon already being inflamed.
Asbestos and Colon/Colorectal Cancer
A study done by the Yale University School of Medicine determined a link between asbestos and colon cancer. In this study, two groups of men were analyzed and compared: smokers who had been exposed to asbestos, and heavy smokers with no known asbestos exposure. The first group was comprised of 1,839 smokers who had been exposed to asbestos. These men worked as plumbers, insulators, sheet metal workers, electricians, and ship fitters. The second group was much larger – with 7,924 individual studied. These men were classified as heavy smokers that have never been exposed to asbestos. Over the course of 12 years, Yale University School of Medicine followed the medical histories of each one of the test subjects. Results showed that smokers, who were exposed to asbestos over a period of 10 to 30 years, had a 36% higher rate of colon cancer. Asbestos-exposed smokers found to have pleura related issues such as pleural thickening or calcification were shown to have a 54% higher risk of colon cancer than those heavy smokers who were not exposed to asbestos.
Asbestos has small, almost invisible, needle- like fibers that are easily inhaled. These fibers are typically embedded in the lining of the lungs, and can cause tumors which eventually escalate to various types of lung cancer. In the case of colon cancer, the theory is that some of the inhaled asbestos fibers by-pass the lung and are swallowed into the stomach or enter through the blood stream. Asbestos is then able to become embedded in the lining of colon wall and tumors may develop.
Diet and exercise also play a role in the development of colon cancer. Overweight people and those who do not consume enough fiber and calcium are at risk for colorectal cancer. Those who consume too much fat, alcohol, and are smokers, are also at a higher risk for developing the cancer. A lack of exercise may also pose a threat.
Signs and Symptoms
According to the United States National Library of Medicine the following are symptoms of colorectal cancer:
- Diarrhea, constipation
- Nausea, vomiting
- A feeling that your bowel does not completely empty
- Bloody stools (bright red or dark red)
- Frequent gas, painful cramps, bloating, or feeling full
- Weight loss
As with most cancers, symptoms are dependent on the placement of the tumor. With colon cancer, tumor placement on the bowel and metastasis can determine which symptoms will occur.
Diagnosis and Treatment
The following tests are commonly used by doctors in diagnosing colorectal cancer:
- A colonoscopy is a type of screening where the doctor examines the inner lining of the large intestine. A thin, flexible tube called a colonoscope is used to look at the entire rectum while the patient is sedated. The purpose of this procedure is to find ulcers, polyps, tumors, bleeding, and inflammation.
- Similar to a colonoscopy, sigmoidoscopy is also a procedure in which a thin, tubular instrument with a light and lens is inserted into the rectum to check for polyps, tumors and any other general abnormalities. This procedure looks at the area of the colon called the sigmoid colon, which is the section of colon that connects to the rectum (making an “S” shape).
- A biopsy is one of the most common procedures used to detect cancer in the body. Typically, a small amount of tissue is removed, sent to a laboratory to be tested and then analyzed by a pathologist. Biopsies are considered to be very accurate in determining if there are any cancerous cells; it is the only procedure than can make a definite colorectal cancer diagnosis. For a colon cancer diagnosis, a biopsy is typically performed during a colonoscopy.
- Blood Test
- Colorectal cancer can often cause bleeding into the large intestine, which is why bloody stools are a common symptom. To determine if the large intestine is bleeding, a blood test is performed. This blood test counts the number of red blood cells and if hemoglobin levels are low, then a cancer diagnosis must be explored as cancer causes the body to produce fewer red blood cells. Blood tests are also used to test the liver, since colorectal cancer commonly spreads to that organ. Colorectal cancer cells sometimes produce something called tumor markers. These tumor markers appear in the blood; the most common for colorectal cancer being carcinoembryonic antigen (CEA) and CA 19-9. However, if an individual tests positive for these tumor markers, it doesn’t necessarily mean that he/she has colorectal cancer. Tumor marker levels can be abnormal for reasons other than cancer, which is why it is not used to solely diagnose colorectal cancer. Tumor markers are typically used in patients who have already been diagnosed with colorectal cancer to help monitor the cancer and treatment.
- Molecular Testing of the Tumor
- Laboratory testing on a tumor will help to identify certain causation factors such as genetics, diet, proteins or any other factors that may be tumor specific.
- Computed Tomography (CT or CAT) scan
- A CT scan for someone who might have colon cancer is useful because it is accurate in determining if there are tumors and where the tumors are placed. The CT scan creates multiple 3-D pictures from different angles, using x-rays. These pictures are then combined to determine abnormalities in the body. A CT scan can also measure tumor size and if the tumor has spread to other parts of the body like the liver or the lungs.
- Soundwaves can also provide images of internal organs – this procedure is called an ultrasound. Using an instrument called a transducer, soundwaves are created. Images are then produced once the sound bounces off the organs. An endorectal ultrasound is used to discover the depth and the growth of rectal cancer; however, it is not a good source in determining metastasis. However, an intraoperative ultrasound test is extremely useful in detecting the spread of colorectal cancer to other organs, such as the liver, because during surgery, a transducer is placed directly on the surface of the liver.
- Magnetic Resonance Imaging (MRI)
- An MRI produces images of the body much like a CT scan and an ultrasound, but an MRI does not use x-rays or soundwaves to create these images. Instead, an MRI uses magnetic fields. A patient can consume (or have injected) a special dye that under an MRI can help produce clearer images. An MRI is the most accurate imaging test in terms of finding colorectal cancer growth.
- An angiography is a type of x-ray examination that looks at person’s blood vessels. Before the x-ray is taken, a contrast dye in injected into an artery. This allows an outline of the blood vessels to appear once the x-ray is taken. The purpose of this type of examination is to show the arteries that are supplying blood to the tumors so better treatment can be administered.
- Barium Enema
- This type of procedure is similar to angiography in that a contrast liquid is inserted into a specific location to produce a better image once examined. In this procedure, a liquid that contains barium (which is a silver/white metallic compound) is inserted into the rectum. Then, a series of x-rays are taken of the lower gastrointestinal tract. The barium flows up through the colon allowing for a clearer image to determine abnormalities.
Treatment is based upon the stage of the cancer. Colorectal cancer is typically divided into four stages; with stage one being the least aggressive and stage four, the most.
- Stage 1 – Cancer had not spread anywhere outside the colon, but has impacted several layers of the colon
- Stage 2 – Cancer may have spread to nearby tissue, but has not affected the lymph nodes yet.
- Stage 3 – Cancer has spread to the lymph nodes, but not to other parts of the body
- Stage 4 – Cancer has spread to other organs in the body; most commonly the liver
Surgery is recommended in the early stages of cancer because most or all of the cancer is able to be removed, leaving the patient cancer-free. However, surgery is also an option for those in the more serious stages.
- A colonoscopy can be used to diagnose if one has colon cancer, but it can also be used to remove any polyps found as long as the polyps are small and in a localized area. This happens in the early stage of the cancer.
- Local Excision
- A cutting tool is inserted through the rectum and into the colon and the cancer is cut out. This happens in the early stage of the cancer and avoids the doctor having to cut the abdominal wall.
- Surgery to remove a polyp is called a polypectomy. Like local excision, a polypectomy can be performed without cutting through the abdominal wall and the cancer is cut out by inserting a tool through the rectum to remove the polyp.
- A colectomy is an operation that removed all or a portion of the colon. If a partial colectomy is done, then the doctor will then preform a procedure called anastomosis, where the healthy sections of the large intestine are then sewn together. If a full colectomy is performed, or anastomosis cannot be done, the doctor will then conduct a colostomy.
- The purpose of a colostomy is to provide another path for waste to leave the body since the colon has been removed or incapable of being sewn back together. An opening (stoma) is made outside the body that connects to the colon. A bag is then placed around this opening to collect waste. A colostomy can be reversed if it is used specifically during the healing process. However, it can also be permanent if the entire lower half of the colon is removed.
- A type of treatment that freezes and destroys abnormal tissue. This procedure either uses very cold liquid or an instrument called a cryoprobe that has been cooled with liquid nitrogen, liquid nitrous oxide, or compressed argon gas.
The following are the most common chemotherapy treatments for colorectal cancer according to the American Cancer Society:
- 5-Fluorouracil (5-FU)
- Capecitabine (Xeloda)
- Irinotecan (Camptosar)
- Oxaliplatin (Eloxatin)
- Trifluridine and tipiracil (Lonsurf)
- Chemotherapy can be used during different times when treating colorectal cancer, either before or after surgery, or instead of surgery.
- Neoadjuvant Chemotherapy – Typically used in rectal cancer, chemotherapy is given to patients before surgery to attempt to shrink tumors to theoretically make surgery easier.
- Adjuvant Chemotherapy – Chemotherapy that is given to patients after surgery in hope of catching and destroying any cancer that surgery may have missed. Some cancer cells could be too small to see or may have escaped and settled into other parts of the body.
When cancer has spread to other organs, chemotherapy isn’t likely to cure the cancer; however, it can shrink tumors, alleviate symptoms and help patients live longer. Colorectal cancer commonly spreads to the liver in the more advanced stages of the cancer.
Often used in conjunction with chemotherapy, radiation uses high-energy rays to break down and destroy cancer cells. Used either before or after surgery, radiation can also be helpful in controlling the spread of cancer in those who are not healthy enough for surgery and is a more common treatment if the cancer has spread to more complicated areas, such as the brain.
For colorectal cancers, there are different types of radiation that can be used as treatment:
- External Beam Radiation Therapy
- Much like getting an x-ray, this type of radiation therapy targets the cancer from a machine that is outside the body. The radiation is much more aggressive when focused on a certain area or tumor. This type of radiation is primarily used to fight colorectal cancer.
- Internal Radiation Therapy (Brachytherapy)
- Internal radiation therapy is when a radioactive source is inserted into your rectum in hopes to better target the cancer without damaging any healthy tissue that sometimes surround the tumors. There are two types of internal radiation therapy:
- Endocavitary radiation therapy
- High-intensity radiation is delivered for a few moments through a small device that is inserted through the anus, and into the rectum.
- Interstitial brachytherapy
- A small tube is inserted into the rectum so it directly contacts the cancer. Then, tiny “radioactive pellets” are placed into the tube for several minutes. Since it is directly hitting the cancer, the radiation does not need to travel far and surrounding tissue is less likely to be affected.
- Targeted Therapy
- Targeted therapy treatments are developed based upon something new a researcher or a scientist has discovered that could be the key in finding successful treatment. These treatments are the latest drugs developed and are contingent on the findings of a scientist or researcher. The most common targeted therapy treatment for colorectal cancer is as follows:
- Bevacizumab (Avastin)
- Ramucirumab (Cyramza)
- Ziv-aflibercept (Zaltrap)
The overall survival of colon cancer is dependent upon the stage of cancer. Those who are in the lower stages of the cancer have a higher survival rate. The following survival statistics are based upon a five-year period from the National Cancer Institute:
- Stage I – 93%
- Stage II – 72% to 85%
- Stage III – 44% to 83%
- Stage IV – 8%
Other factors such as the quality of surgery, the number of lymph nodes affected and if the cancer had spread to other organs, also affect the prognosis of colorectal cancer.