Cancer is one of the leading causes of death in the United States, and colorectal cancer is the third most common cancer diagnosed in the United States. Colorectal cancer originates in the colon (the large intestine) or the rectum, and is for this reason also called colon cancer or rectal cancer depending on its starting point.
Colon cancer affects men and women, and the American Cancer Society estimates that 101,420 new cases of colon cancer and 44,180 new cases of rectal cancer will be diagnosed in the U.S. in 2019. Let's explore the causes, symptoms, and treatments for colon cancer, as well as the screening options that can dramatically up survival odds.
What Causes Colon Cancer?
Most colon cancers are caused by colon polyps. Polyps are growths on the colon or rectum and can be malignant or benign. Benign polyps shouldn’t be ignored, though, as they can sometimes become cancerous over time. Polyps are more likely to become cancerous if any of the following applies:
- A polyp is larger than 1 centimeter.
- More than two polyps are found.
- Dysplasia is present after polyp removal. Dysplasia means that either the removed polyp or the lining of the colon or rectum has a spot where the cells look abnormal but are not considered cancerous cells yet. The abnormal cells make dysplasia a precancerous condition.
Once a polyp is cancerous, the cancer cells can spread from the polyp to the lining of the colon or rectum. From there, it can spread to blood vessels, lymph nodes, and potentially to other parts of the body.
Like other cancers, there are four stages of colorectal cancer. There is a stage zero, however, so one could technically say there are five stages. The higher the stage number, the further the cancer has spread in the body.
Colon Cancer Risk Factors
Some people may be at an increased risk of developing colorectal cancer. Factors that contribute to a higher risk for colorectal cancer include age, race, ethnicity, genetics, personal and family medical history, and lifestyle choices.
Colorectal cancer most often occurs after age 50. However, that doesn’t mean that it cannot develop before age 50. Colon cancer can develop at any age.
A personal history of previous colorectal cancer, colorectal polyps, type 2 diabetes, or inflammatory bowel diseases such as Crohn's disease and ulcerative colitis increase one’s chances of developing colorectal cancer or getting colorectal cancer again. A family history of colorectal cancer or precancerous polyps also increases one’s chances of developing colorectal cancer. Family history refers to first-degree relatives, meaning parents, siblings, or children who have been diagnosed with colorectal cancer or polyps.
Race and Ethnicity
For reasons unknown, colorectal cancer is most common in the United States amongst African Americans. Globally, Jews of Eastern European descent have a greater risk of developing colorectal cancer than any other ethnic group.
In some cases, colorectal cancer is linked to hereditary syndromes that get passed down in family members. Possible genetic causes of colorectal cancer include:
- Lynch Syndrome
- Familial Adenomatous Polyposis (FAP)
- Peutz-Jeghers Syndrome (PJS)
- MYH-associated Polyposis (MAP)
One cannot change one’s personal medical history, family history, age, or genetics. There are, however, certain lifestyle choices that carry an increased risk of colorectal cancer and can be changed to lower the risk. These include:
- Weight: Being overweight or obese increases the risk of developing colorectal cancer.
- Physical activity: Being active can help lower the risk of colorectal cancer while being inactive increases the risk.
- Diet: Diets that are high in red meats and processed meats increase the risk of developing colorectal cancer.
- Smoking: Smokers are more likely than non-smokers to develop various types of cancer, including lung cancer and colorectal cancer.
- Heavy alcohol use: According to the American Cancer Society, moderate to heavy drinking has been linked to multiple types of cancer, including colorectal cancer.
Colon Cancer Symptoms
Symptoms of colorectal cancer may not appear right away. By the time symptoms do appear, they often include the following:
- Change in bowel habits:
- Narrower stools
- An urge to have a bowel movement that is not relieved by actually having one
- Rectal bleeding with bright red blood
- Blood in the stool or darkened stool
- Cramping and/or abdominal pain
- Weight loss without change to diet or exercise
- Onset of anemia due to blood loss and bleeding into the digestive tract
Colon Cancer Screening and Diagnosis
Early detection is key for surviving colon cancer. Thankfully, there are many ways to screen for colorectal cancer and prevent colon cancer from developing.
If you are at average risk of colon cancer, most doctors recommend beginning colorectal cancer screening at age 50. However, if you have an increased risk for colon cancer, such as an underlying medical condition or family history of colon cancer or colon polyps, then your doctor may order a colonoscopy or other screening test earlier. The American Cancer Society recommends screening for colon cancer at age 45 with either a stool-based test or a visual exam of the rectum.
Colorectal screening tests include the following.
Although there's some legwork involved with a colonoscopy (you'll have to fast from solid food and drink a laxative), it's the most thorough screening option because your doctor can view your entire colon and rectum, take biopsies of any suspicious tissues, and remove polyps. If no polyps are found, you're good to go for another 10 years, but if polyps are found and removed or if there are any other risk factors found, your doctor will recommend a followup colonoscopy within 5 years time.
CT Colonography (Virtual Colonoscopy)
According to the National Cancer Institute, clinical trials are underway testing the efficacy of virtual colonoscopy compared to other colon cancer screening tests.
Not as invasive as a traditional colonoscopy, virtual colonoscopy uses a CT scan to generate pictures of the colon and rectum that can indicate polyps or other abnormalities. CT colonography is usually reserved for patients who aren't candidates for a colonoscopy, such as those with a bowel obstruction, a history of colon cancer or polyps, a chronic inflammatory bowel disease, or acute diverticulitis.
A flexible sigmoidoscopy is used as a cancer screening tool every 5 years (or 10 with an annual fecal test). It requires inserting a short, thin, flexible, lighted tube into the rectum to look for polyps. While the doctor can see all the rectum, only about a third of the colon is visible, and it's not the most widely used screening test for colon cancer.
Fecal Immunochemical Test (FIT)
Recommended annually for the early detection of colorectal cancer, the FIT, also called an immunochemical fecal occult blood test (iFOBT), checks for hidden blood in the stool. It's easy to collect a sample at home using cards or tubes, and you don't have to diet or take laxatives for this stool-based test. If results return positive, a colonoscopy will be required.
Guaiac-Based Fecal Occult Blood Test (gFOBT)
Using a chemical reaction, the guaiac-based fecal occult blood test (gFOBT) looks for blood in the stool, but, like the FIT test, the gFOBT cannot assess where in the digestive tract the blood originates from—the colon or the stomach, for instance.
The gFOBT is recommended each year and requires some dietary modifications before collecting the multiple stool samples. Your doctor may instruct you to avoid NSAIDs a week before, and vitamin C over 250 mg as well as red meat 3 days before testing.
Stool DNA test
Colorectal cancer or polyp cells can produce DNA changes in specific genes, and these mutated cells can show up in stool. Cologuard® is a stool DNA test that can detect these DNA mutations in blood in the stool. You can collect samples with an at-home kit every 3 years. If results show DNA changes, then a colonoscopy will be required.
In addition to the above stool-based and visual tests, your doctor may order a blood test to check for a substance produced by cancer cells called carcinoembryonic antigen (CEA).
Colon Cancer Treatment
The treatment prescribed for colon cancer will depend upon the stage of the cancer. Common treatments include surgery and chemotherapy.
If caught in the early stages, colorectal cancer can sometimes be treated with surgery alone, such as removal of the cancerous polyps. As the cancer progresses, however, more involved surgeries may become necessary, including removing part of the colon. Common surgeries used to treat colorectal cancer include:
- Polypectomy to remove cancerous polyps
- Local excision to remove cancer from the inside lining of the colon
- Partial or total colectomy to remove part or all of the colon as well as nearby lymph nodes
- Surgery to remove small cancer spots on other organs where the cancer has spread
Chemotherapy is a medical protocol that uses drugs to kill cancer cells. It is a common treatment in many types of cancer, including colorectal cancer. Most patients who have been prescribed chemotherapy usually receive multiple rounds of the treatment and have to wait around two to four weeks between treatments to give their bodies a chance to rest and recover.
Chemotherapy may be given after cancer removal surgery to ensure that no cancer cells are left behind. It can also be given before surgery in an attempt to shrink large tumors. Shrinking large tumors increases the likelihood of successful tumor removal surgery. There are different ways that a patient may receive chemotherapy, including:
- Systemic: Drugs are injected or taken orally to get the drugs into the bloodstream and distributed throughout the body.
- Regional: Drugs are focused on the specific part of the body that is housing the tumor or cancer cells.
Common side effects of chemotherapy include:
- Hair loss
- Mouth sores, or ulcers
- Decreased appetite
- Nausea and vomiting
- Reduced white blood cell count, which increases the likelihood of infections
- Reduced blood platelets, which increases easy bruising and bleeding
Radiation therapy is often used as a treatment option to relieve pain and discomfort when surgery is not possible. It can also be combined with chemotherapy for a targeted approach called chemoradiation or chemoradiotherapy.
More often prescribed for rectal than colon cancer, radiation therapy uses X-rays or protons (high-energy rays) to destroy cancer cells. For example, radiation is used to shrink cancerous tumors before surgery.
Colon Cancer Prevention
While there are variables, such as age and family history, that cannot be changed, colon cancer is preventable in the sense that a healthy, high-fiber, whole foods diet, consistent exercise, and healthy lifestyle (no smoking or drinking) can go a long way towards keeping your colon strong and healthy.
Although there will be a predicted 51,020 cancer deaths in America in 2019, the mortality rates from colorectal cancer have been steadily declining for decades, in large part due to screening tests and early detection. Discuss your colorectal cancer screening options with your health care provider at your annual physical exam, or sooner if you are exhibiting symptoms.