Rectal cancer is cancer that starts in the rectum. The rectum consists of the last few inches of the large intestine. It connects to the colon on one end and the anus on the other.
The body moves waste, called stool, through all three structures before expelling it through the anus.
Rectal cancer and colon cancer start the same way and share many risk factors and symptoms. The two diseases are often referred to together as colorectal cancer. There are some significant differences between the two diseases, though.
Rectal cancer that has not spread to distant parts of the body is also treated with surgery. For some patients, radiation therapy and chemotherapy are used to decrease the risk of the cancer returning after treatment. In some cases, radiation therapy and chemotherapy can reduce the need for surgery. Rectal cancer surgery can be more complex than colon cancer surgery.
How does rectal cancer start?
Rectal cancer usually starts as a polyp. Polyps are small overgrowths in the tissue lining the colon or rectum. Polyps are not cancer.
Some polyps can turn into cancer over time. Most of these polyps are adenomas, which begin in mucus-producing gland cells that line the intestine and other organs. Adenomas are considered pre-cancerous growths.
It can take several years for an adenoma to develop into cancer. When it does, the cancer is called an adenocarcinoma. This is the most common type of rectal cancer.
There are other, rarer types of rectal cancer, including rectal neuroendocrine tumors and rectal cancers that involve the cells of the anus.
There are more than 150,000 combined colon and rectal cancer diagnoses in the United States each year. As of 2018, the disease’s five-year survival rate is about 65%. This figure does not include people diagnosed more recently, who could benefit from new treatments.
Young-onset colorectal cancer
Historically, most cases of colorectal cancer have been in people over age 55. In recent years, there has been an increase in diagnoses among people under age 55. UT MD Anderson’s Young-onset Colorectal Cancer Program offers specialized services for these patients. Services include fertility care, genetic testing and counseling, as well as support groups for young adults.
Rectal cancer screening
Most precancerous polyps produce few, if any, symptoms, so it is important to get screened regularly for rectal cancer. Rectal cancer screenings allow your doctor to find and remove polyps before they turn into cancer. Screening can prevent most cases of rectal cancer cases. It can also catch rectal cancer early, when treatments are more likely to be successful.
- Learn more about rectal cancer screenings
Rectal cancer risk factors
Anything that increases your chance of getting colorectal cancer is a risk factor. Colorectal cancer risk factors include:
- Age: More than 75% of colorectal cancer cases are diagnosed in patients age 55 and older. The median age at diagnosis is 66 years old. However, the rate of colorectal cancer diagnosed in adults less than 55 years old has increased in recent years.
- Race: African Americans have the highest rate of colorectal cancer among all racial groups in the United States.
- Family history: People whose relatives have had colorectal cancer or colorectal polyps have an increased risk of colorectal cancer.
- Inflammatory bowel disease: Patients with conditions that include Crohn’s disease or chronic ulcerative colitis are more likely to develop colon cancer. Learn more about inflammatory bowel disease and colorectal cancer.
- Personal history of colorectal cancer or polyps: People who have previously had colorectal cancer or colon polyps are at an increased risk of developing colorectal cancer.
- Hereditary cancer syndromes: Some genetic changes can be inherited and increase your risk for certain types of cancer. Inherited syndromes including hereditary nonpolyposis colorectal cancer, or Lynch syndrome, and familial adenomatous polyposis may put you at higher risk for developing colorectal cancer. Learn more about hereditary cancer syndromes.
- Diet: A diet heavy in red meat, processed meats, or meats cooked at very high heat can increase a person’s rectal cancer risk.
- Obesity: Obesity increases a person’s chance of developing many different diseases, including colorectal cancer.
- Sedentary lifestyle: A lack of movement and exercise is a risk factor for colorectal cancer.
- Cigarette smoking: Tobacco use, including cigarettes and chewing tobacco, is a colorectal cancer risk factor.
- Drinking too much alcohol: Heavy drinkers are at an increased risk for colorectal cancer.
For patients concerned about inherited family syndromes that cause colorectal cancer, we offer advanced genetic testing and counseling to help understand your risk.
Rectal cancer prevention
Lifestyle choices that may decrease your risk of getting rectal cancer include:
- Regular screening tests
- Staying at a healthy weight
- Regular exercise
- Eating a healthy diet with lots of fruits and vegetables
- Avoiding cigarette smoking
- Drinking alcohol only in moderation
Learn more about rectal cancer:
Cancer in the sigmoid colon: What it means when colon cancer is on the left side
The sigmoid colon is the part of the large intestine (colon) closest to the rectum. It absorbs water from stool and pushes the stool to the rectum and anus until it’s ready to be expelled when you use the bathroom.
Colorectal cancer is an umbrella term for colon cancer and rectal cancer. Studies have shown that colorectal cancer is more common in the sigmoid colon, which is on the left side, along with the descending colon and rectum. The rectum is also considered the left side even though it’s not part of the colon.
Gastrointestinal medical oncologist Kanwal Raghav, M.D., estimates that about 70% of colorectal cancers are diagnosed on the left side.
“It’s unclear why colon cancer starts in a particular location, although some explanations exist,” says Raghav. “However, left-side colon cancers are more common than right-side colon cancers.”
The colon starts at the cecum, which is on the right side. It goes up to the ascending colon, across the body to the transverse colon and down to the descending colon and sigmoid colon, which are on the left side.
We spoke with Raghav to learn more about the differences between left-side and right-side colon cancer. Here’s what he shared.
It’s common for left-side tumors to cause symptoms.
It's common for people with left-side colorectal cancer to have changes in their bowel habits or blood in their stool. People with right-side tumors often show fewer symptoms.
Left-side tumors and right-side tumors have different genetic characteristics.
Tumors that develop on the left side of the colon have more mutations of tumor-suppressing genes, like APC and TP53. These genes help prevent tumors from growing. Mutations in these genes make you more likely to develop certain cancers, including colon cancer.
Tumors that develop on the right side of the colon are more likely in people who have hereditary cancer syndromes. These include high microsatellite instability (MSI-high) – also referred to as DNA mismatch repair deficiency (dMMR) – and Lynch syndrome.
Left-side tumors are easier to detect during a colonoscopy.
During a colonoscopy, your doctor examines the walls and lining of your colon, including the sigmoid colon, by inserting a flexible scope into your rectum and around your large intestine. Doctors examine the left side first since it’s closer to where the scope is inserted. Colorectal cancer usually starts as a polyp in the colon or rectum.
Left-side tumors often present as polypoid lesions, which protrude into the lumen of the gastrointestinal tract and are easier to see. Colonoscopies are good at detecting these polyps, which is why getting this routine screening is so important.
Many polyps on the right side of the colon are sessile serrated adenomas. These are flat and harder to detect during a colonoscopy. Because of this, right-side colon cancers are often diagnosed at advanced stages and may be harder to treat.
Colonoscopy prep is important because your colon will need to be completely clean of any stool, so your doctor can easily see both the left and right side of your colon.
The side on which cancer develops helps determine your treatment.
Overall, left-side tumors have a better prognosis than right-side tumors. This is because colon cancer on the left side responds better to chemotherapy and targeted therapies, like anti-EGFR and HER2 drugs.
Right-side tumors tend to have more genetic mutations, which are often associated with more aggressive cancers. Right-side tumors are also harder to detect, so they’re often diagnosed when the disease is more advanced. Recently, immunotherapy has been effective in treating these cancers because the body can recognize the abnormal cells and attack them. Immunotherapy has helped improve the prognosis for patients with stage IV right-side colon cancer.
Your doctor and care team will work together to develop the best treatment plan for you.
Knowledge of left-side and right-side colon cancer leads to treatment advances.
We’ve been treating colorectal cancer for a long time. But only in the last four or five years have we really started to understand the differences between colon cancer that develops on the left side versus the right side. Before then, it wasn’t as commonly acknowledged.
Over the years, we have learned that colon cancer can’t be viewed as one disease. We’re now looking at it as a complex disease with many subtypes and trying to develop targeted and personalized therapies that can be used depending on the specific type people have. Slowly and steadily, we are moving the bar for personalized therapy in colorectal cancer. And I think the location of the cancer – left side versus right side, including the sigmoid colon – is a part of that.
Request an appointment at MD Anderson online or call 1-877-632-6789.
Why choose UT MD Anderson for rectal cancer treatment?
At UT MD Anderson's Colorectal Center, your rectal cancer treatment is personalized to provide the best outcomes, while focusing on your quality of life. We offer leading-edge treatments for rectal cancer, including advanced minimally invasive surgeries that provide successful treatment with less impact on you and sphincter-preserving surgeries, eliminating the need for a colostomy bag.
Multidisciplinary team approach
Rectal cancer treatment at UT MD Anderson is provided by a team of experts, including medical oncologists, surgeons, radiation oncologists, gastroenterologists, radiologists, clinical nurses and mid-level providers. They discuss your case and develop a treatment designed to attack your cancer while minimizing side effects.
Supplementing your clinical care, UT MD Anderson also provides nutrition counseling, pain management, psychological support, wound management and other services.
Younger patients can also receive specialized support through our Young-onset Colorectal Cancer Program. This program offers services like genetic counseling and testing, fertility preservation and young-adult support groups.
In addition, our advanced knowledge in cancer genetics can help diagnose and treat inherited family syndromes that may increase your risk of rectal cancer. This expertise also helps us work with you to plan the most effective treatment for your specific condition.
For patients who have been successfully treated for rectal cancer and are being monitored for recurrence, our tumor Intercept program also offers circulating tumor DNA testing. Patients may even be matched with clinical trials to monitor for or prevent the cancer’s return. This test can help doctors diagnose a recurrence long before it shows up in an imaging exam.
Leading-edge advancements
As one of the world’s largest cancer research centers, UT MD Anderson is a leading center for the investigation into new methods of rectal cancer treatment and diagnosis. Through our clinical trials, this research can give patients access to treatments and procedures not found anywhere else.
And at UT MD Anderson you'll also be surrounded by the strength of one of the nation's largest and most experienced cancer centers. From support groups to counseling to integrative medicine care, we have all the services needed to treat not just the disease, but the whole person.
When it comes to dealing with cancer, it is what is it and you’ve got to seek the best care that you can.
MD Anderson's Colorectal Center is located in the Dan L. Duncan Building.
