October 7, 2021 - read ≈ 18 min
Vanessa M. Welten MD, MPH
MD, MSc, FACS
Colorectal Cancer Overview
Colorectal cancer is cancer that affects the large intestine. It is the third most common cancer cause of cancer and the second leading cause of cancer death among both males and females in the United States.1 The large intestine can be divided into two main parts: the colon and the rectum. Thus, the term “colorectal cancer” encompasses both colon and rectal cancers. The colon begins immediately after your small intestine and ends with your rectum. The rectum is the last part of the large intestine before the anus.
Colorectal cancer typically begins as a “polyp” on the inner lining of the colon or rectum. A polyp is an outgrowth that develops when abnormal cells in your body replicate quickly. If these polyps continue to grow, they can develop into cancer and ultimately invade the wall of the colon or rectum and potentially spread to other parts of your body.
Colorectal Cancer Prevention and Screening
A screening test for colorectal cancer is an evaluation done to detect polyps or cancer in a person without symptoms. Polyps are considered “pre-cancerous”, such that colorectal cancer can be prevented if a polyp is detected early and removed, colon or rectal cancer can be prevented. After the age of 50, polyps are very common, even if you are otherwise healthy and even if you do not have a family history of colorectal cancer. You may have polyps even if you feel well and have no symptoms. For these reasons, it is really important to undergo colorectal cancer screening at consistent intervals as directed by your doctor, in order to detect polyps early and have them removed as needed.
There are many approved colorectal screening tests for adults in the United States. All average-risk adults in the United States should be screened between the age of 45 and 75 years old.2 Average-risk means that you do not have any risk factors, symptoms, personal or family history that put you more at risk for developing colorectal cancer.
There are 7 recommended for colorectal cancer screening.2 All tests have associated benefits and risks. The different screening options with their associated benefits and risks are the following:
- Colonoscopy, every 10 years
A colonoscopy is a procedure to evaluate your entire colon and rectum for polyps or other abnormalities. During this procedure, a long thin camera is insert into your rectum and is gently advanced all the way to the end of your colon. The day prior to the procedure, patients are instructed to take a combination of stool softeners and laxatives to clean their colon and rectum of any stool to optimize the colonoscopy evaluation. At the time of the procedure, patients are administered mild sedation medications to keep them relaxed and comfortable. The procedure is performed by a trained physician and typically lasts 30-45 minutes.
If any polyps or other abnormalities are identified during the colonoscopy, these are removed and sent for evaluation. The removed polyps or tissue are examined closely to look for cancerous cells.
The benefit of colonoscopy is that it is the most thorough and accurate test to identify polyps or other pre-cancerous lesions. Colonoscopy allows removing abnormal tissue upon identification and sending it for evaluation immediately. It is only necessary every 10 years, unless an abnormality is identified that needs an intervention. The drawbacks of the colonoscopy include the preparation with laxatives and stool softeners, as well as the sedation required for the procedure. Colonoscopy also has a risk of injuring the colon or rectum, though this is very rare.
- Flexible sigmoidoscopy, every 5 years
A flexible sigmoidoscopy is similar to a colonoscopy, but it only evaluates the rectum and the last third part of the colon, called the sigmoid colon. It also involves the insertion of a thin camera into the rectum; however, the camera is only advanced as far as through the sigmoid colon. Patients are provided with relaxing medications to keep them comfortable. The procedure takes about 20 to 30 minutes to complete.
If any polyps or abnormalities are identified, they are removed and subsequently evaluated for cancerous cells.
The benefit of flexible sigmoidoscopy is that it is very accurate at identifying polyps or other pre-cancerous lesions in the sigmoid colon or rectum. If any such lesions are identified, they can be removed and sent for evaluation immediately. The main drawback to flexible sigmoidoscopy is that it does not evaluate about two-thirds of the colon, and therefore there is a risk of missing some polyps that are located in the earlier parts of the colon. Like colonoscopy, the procedure requires sedation and also carries the small risk of injury to the colon or rectum.
- Fecal DNA test, every 1 to 3 years
The fecal DNA test involves collecting a stool sample and testing it for mutations concerning for colorectal cancer. The patient collects a sample as directed and return it to their doctor’s office for testing.
The benefits of this test include the ease of sample collection, which does not require laxative preparation, sedation, or carry the risk of injury. However, the test is not as accurate at identifying pre-cancerous lesions as colonoscopy or sigmoidoscopy. If there is concern for a pre-cancerous lesion, a follow-up colonoscopy will be required to look for and sample any concerning areas in the colon or rectum.
- Fecal occult blood test (FOBT), every year
Fecal occult blood test involves collecting a stool sample and testing it for microscopic blood particles. The patient collects a sample as directed and return it to their doctor’s office for testing.
The benefits and draw backs for FOBT are similar to that of the fecal DNA test.
- Fecal immunohistochemistry test (FIT), every year
Fecal immunohistochemistry test, or FIT, also assesses for microscopic blood particles. For this test, a stool sample is combined with a liquid containing antibody molecules that can attach themselves to blood particles. If there is blood present in the sample, this will be detected when the mixture is processed through a specialized instrument that identifies the attached antibodies. The patient collects a sample as directed and return it to their doctor’s office for testing.
The benefits and draw backs for FIT are similar to that of the fecal DNA test.
- Computed tomography (CT) colonography, also referred to virtual colonoscopy, every 5 years
CT colonography, or virtual colonoscopy, involves taking a series of x-ray images of the colon and rectum while the colon and rectum are inflated by air. The images are combined by the CT machine in a way to detect any colorectal polyps. For this procedure, air is injected into the rectum in order to inflate the colon and rectum for the images. Prior to the virtual colonoscopy, patients are instructed to take a combination of stool softeners and laxatives to clean their colon and rectum of any stool to optimize the quality of the images. Unlike a standard colonoscopy, the virtual colonoscopy does not require any sedating medications. The process takes about 10-15 minutes to complete.
The benefits of the virtual colonoscopy include the fact that the test is less invasive than colonoscopy and flexible sigmoidoscopy, and therefore does not carry the same risk of injuring the colon or rectum. Though it is not as accurate as colonoscopy at identifying concerning polyps, it is more accurate than the stool tests (fecal DNA, FOBT, and FIT). No sedation is required for this test. The drawbacks of virtual colonoscopy include the radiation exposure involved in the serial image taking and the laxative preparation required before the imaging. If a polyp is identified, a follow-up colonoscopy will be required to look for and sample any concerning areas in the colon or rectum.
- Flexible sigmoidoscopy, every 10 years, together with FIT, every year
This final screening option is a combination of the flexible sigmoidoscopy and the FIT tests previously described, at the time intervals stated above.
The benefits and drawbacks of this combination screening methods include those listed for flexible sigmoidoscopy and FIT, respectively. One additional benefit is the fact that the combination of the two tests allows increasing the accuracy of identifying colorectal cancer than either the flexible sigmoidoscopy or the FIT test alone, and therefore the flexible sigmoidoscopy is only required at 10-year intervals rather than at 5-year intervals. Further, the addition of the FIT testing to flexible sigmoidoscopy may help identifying concerning lesions that are located in the earlier parts of the colon that would be missed on flexible sigmoidoscopy alone. If the FIT testing is positive, a follow-up colonoscopy will be required to look for and sample any concerning areas in the colon or rectum.
Though there are many options for screening described, with various associated benefits and risks, the most strongly recommended screening test is colonoscopy every 10 years. This test allows for the most thorough examination of the entire colon and immediate removal of any polyps or abnormalities identified. However, it is reasonable for patients to choose to pursue other screening options according to their comfort and preferences in consultation with their doctor.
Your doctor may recommend that you have a screening test earlier than 45 years of age if you have risk factors that make you more prone to developing colorectal cancer. Factors that increase your risk of developing colorectal cancer and that may warrant earlier colorectal cancer screening include: a personal history of inflammatory bowel disease (Crohn’s disease or Ulcerative colitis), family history of colorectal cancer, personal or family history of genetic conditions associated with colorectal cancer (including Familial Adenomatous Polyposis syndrome, Lynch Syndrome, among others).
Symptoms of Colorectal Cancer
Screening tests are performed for patients without symptoms are regular intervals to prevent the development of colorectal cancer. If a patient develops symptoms concerning for colorectal cancer, a patient will require diagnostic tests to investigate the cause of their symptoms. The diagnostic test may involve a colonoscopy that is done near the time of symptom onset, rather than waiting the designated time period according to screening recommendations.
Symptoms of colorectal cancer may include the following: abdominal pain, bleeding from your rectum, change in the regularity of your bowel movements, prolonged diarrhea or constipation, change in the size or appearance of your bowel movements, unintentional weight loss, new fatigue, among others. If you develop any of these symptoms, it is important to speak to your doctor for evaluation.
Risk factors for Colorectal Cancer
There are two kinds of risk factors for colorectal cancer: modifiable and non-modifiable. Modifiable risk factors are things or behaviors that a patient can change about their lifestyle that may increase or decrease the risk of colorectal cancer. Non-modifiable risk factors are things that are out of a patient’s control.
Modifiable risk factors that increase the risk of colorectal cancer include smoking, alcohol intake, obesity, low fiber intake, as well as high fat and red meat intake. Decreasing these lifestyle factors can reduce the risk of colorectal cancer. Unlike non-modifiable risk factors, modifiable risk factors do not necessarily influence age at which colorectal cancer screening should begin.
Non-modifiable risk factors include those previously mentioned that may warrant earlier colorectal cancer screening. These include personal history of inflammatory bowel disease (Crohn’s or Ulcerative Colitis), family history of colorectal cancer, familial genetic conditions associated with colorectal cancer (such as Familial Adenomatous Polyposis, Lynch Syndrome or others). Other non-modifiable risk factors that increase the risk of colorectal cancer but do not influence the timing of colorectal screening include older age and prior radiation.
Treatment for Colorectal Cancer
If colorectal cancer is diagnosed either as a result of a screening test or following the investigation of new symptoms, treatment will depend on the stage of the cancer.
Depending on how the cancer was diagnosed, the full work-up to determine the stage of the cancer includes: a biopsy of the colon or rectal tumor, as well as a CT scan of your chest, abdomen and pelvis. The biopsy of the tumor will determine how deep the cancer has invaded the wall of the colon or rectum, while the CT scans will determine if the cancer has spread to any other sites of the body.
Colorectal cancer is divided into 5 different stages, in order of increasing severity: stage 0, stage I, stage II, stage III, and stage IV.
- Stage 0 means that the cancer cells have not grown beyond the lining the of colon or rectum.
- Stage I means that the tumor is invading the inner lining but has not gone all the way through the wall of the colon or rectum.
- Stage II means that the tumor has grown through the wall of the colon or rectum, but it has not spread to the nearby lymph nodes.
- Stage III means that that tumor has grown through the wall of the colon or rectum and has also spread to involve the lymph nodes.
- Stage IV means that the tumor has spread to other organs in the body far away from the initial colorectal tumor.
Once the stage of the colorectal cancer has been determined, a treatment plan can be developed. Treatment for colorectal cancer can involve a combination of surgery, chemotherapy, and/or radiation therapy.
For stage 0, the treatment typically involves removal of the polyp only.
For stage I colorectal cancers, the treatment may only involve removal of the polyp. If the polyp was removed completely at the time of diagnosis, then no further treatment is typically needed at that time. If the polyp was removed incompletely or if there the cancer cells have certain concerning features, then surgery to remove part of the colon or rectum may be required.
For colon cancer, this involves removal of part of the colon where the polyp is located, which is called a partial colectomy.
For rectal cancer, the type of surgery needed depends on the size of the polyp that remains. If it is small, the surgery may be performed through the anus to remove the cancerous polyp, which is called a transanal excision. If the remaining polyp is too large or has concerning features, more extensive surgery involving removal of part or all of the rectum may be involved. The type of surgery depends on the location of the polyp within the rectum. If the polyp is close to the colon, part of the rectum is removed, which is called a low anterior resection (LAR) to remove part of the rectum. If the polyp is closer to the anus, the surgery is may involve removal of the entire rectum which is called an abdominoperineal resection (APR). These surgeries will be further described below.
For stage II and III, the treatment differs slightly between colon and rectal cancers.
For stage II cancers located in the colon, the first step of treatment is typically surgery to remove part of the colon where the tumor is located. In most cases of colon cancer surgeries, the colon can be directly re-connected. Some stage II colorectal cancers will then require chemotherapy after their surgery, depending on the specific features of their tumor. Chemotherapy that is administered after surgery is called adjuvant chemotherapy.
For stage III cancers located in the colon, treatment typically involves a combination of surgery and chemotherapy. First, the section of the colon with the tumor is removed and this is followed by adjuvant chemotherapy. In some cases, the tumor may be too extensive to remove surgically at the beginning, and some patients are treated with a combination of chemotherapy and radiation to reduce the size of the tumor before proceeding to surgical removal. Chemotherapy and/or radiation administered before surgery is called neoadjuvant chemotherapy or radiation. The purpose of neoadjuvant chemotherapy and radiation in these cases is to increase the success of surgery to remove the entire tumor.
For stage II and stage III cancers located in the rectum, the treatment typically involves a combination of surgery, chemotherapy, and radiation. In most cases, patients are initially treated with a combination of neoadjuvant chemotherapy and radiation, called chemoradiation, which allows reducing the size of the tumor before surgery. Patients then undergo surgery to remove the rectal tumor.
There are two main types of rectal cancer surgery, depending on the location of the rectal tumor. If the tumor is located close to the colon, patients typically undergo a surgery called low anterior resection (LAR), which involves removal of the section of the rectum with the tumor. In most cases, the colon can be reconnected to the remaining end of the rectum directly. In some cases, if the surgery feels that there is a risk that the connection may not heal properly, they may perform a temporary ileostomy. A temporary ileostomy is when the end of small intestine is connected to an opening in the skin to create an ostomy, and stool is collected in an ostomy bag. Stool from an ileostomy is more liquid in consistency than typical stool. Temporary ileostomies allow time for the connection between the end of the colon and the rectum to heal. The As in the name, they are temporary and in the majority of cases, patients undergo a second surgery to reverse the ileostomy back inside the abdomen and be fully connected.
If the tumor is located lower in the rectum, closer to the anus, patients undergo a surgery called abdominoperineal resection (APR), which involves complete removal of the rectum and the creation of a permanent colostomy. A permanent colostomy is different from a temporary ileostomy in few main ways. First, it is the part of the colon, rather than the small intestine, that is connected to an opening in the skin to create the ostomy. Second, the consistency of stool from colostomy is thicker and has a similar consistency to regular stool, unlike the stool from an ileostomy. Third, the colostomy from this surgery is permanent and is not reversed into the body after a period of time.
For both stage II and III rectal cancer, surgery is typically followed by adjuvant chemotherapy.
For stage IV colon and rectal cancer, the treatment depends on the extent of spread of the disease to other organs. Colorectal cancers most commonly spread to the liver and to the lung. These new areas where the cancer has spread are call metastases.
For colon cancer, if the number of metastases to other organs is limited, surgery may be pursued to remove the main tumor from the colon and to remove the sites of tumor metastases. Chemotherapy may be administered either before and/or after surgery, depending on the size of the metastases, and if it is thought that the chemotherapy will help decrease the size of the main tumor and of the metastases. If the disease
For rectal cancer, if the number of metastases to other organs is limited, surgery may be pursued to remove the rectal tumor in addition to the sites of metastases. This may be accompanied by a combination of chemotherapy and/or radiation therapy administered before the surgery and/or by chemotherapy administered after the surgery. Treatment with chemotherapy and/or radiation before the surgery is to improve the chances of removing all of the tumor sites by decreasing their size before surgery.
In both colon and rectal cancer, if the spread of the disease is too extensive, treatment is typically limited to chemotherapy alone. In this case, surgery is only used if it can help improve some symptoms due to the tumor, such as if the tumor is creating a blockage or too much abdominal discomfort.
In general, the treatment of colorectal cancer involves a team of medical providers who work together to come up with the best treatment plan based on the individual patient’s disease characteristics and treatment goals. The team typically includes a medical oncologist (who guides chemotherapy decisions), a radiologist (who reviews the images that help determine the stage of the disease), a radiation oncologist (who guides radiation therapy decisions), a colorectal surgeon (who guides surgical decisions), and a pathologist (who interprets tumor characteristics).
- NCI. Cancer Stat Facts: Common Cancer Sites. National Cancer Institute: Surveillance, Epidemiology, and End Results Program. Published 2021. Updated 2021. Accessed September 27, 2021.
- USPSTF. Colorectal Cancer: Screening. U.S. Preventive Services Task Force. Recommendation: Colorectal Cancer: Screening Web site. Published 2021. Updated May 18 2021. Accessed September 27, 2021.