Medically reviewed on January 4, 2018
The rectum is the last several inches of the large intestine. It starts at the end of the final segment of your colon and ends when it reaches the short, narrow passage leading to the anus.
Cancer inside the rectum (rectal cancer) and cancer inside the colon (colon cancer) are often referred to together as "colorectal cancer."
While rectal and colon cancers are similar in many ways, their treatments are quite different. This is mainly because the rectum sits in a tight space, barely separated from other organs and structures in the pelvic cavity. As a result, complete surgical removal of rectal cancer is challenging and highly complex. Additional treatment is often needed before or after surgery — or both — to reduce the chance that the cancer will return.
In the past, long-term survival was uncommon for people with rectal cancer, even after extensive treatment. Thanks to treatment advances over the past 30 years, rectal cancer can now, in many cases, be cured.
The rectum is the last several inches of the large intestine. Rectal cancer starts in the lining of the rectum (rectal mucosa).
Common symptoms include:
- A change in your bowel habits, such as diarrhea, constipation or more-frequent bowel movements
- Dark or red blood in stool
- Mucus in stool
- Narrow stool
- Abdominal pain
- Painful bowel movements
- Iron deficiency anemia
- A feeling that your bowel doesn't empty completely
- Unexplained weight loss
- Weakness or fatigue
When to see a doctor
Make an appointment with your doctor if you have symptoms suggesting rectal cancer, particularly blood in your stool or unexplained weight loss.
Rectal cancer occurs when healthy cells in the rectum develop errors in their DNA. In most cases, the cause of these errors is unknown.
Healthy cells grow and divide in an orderly way to keep your body functioning normally. But when a cell's DNA is damaged and becomes cancerous, cells continue to divide — even when new cells aren't needed. As the cells accumulate, they form a tumor.
With time, the cancer cells can grow to invade and destroy normal tissue nearby. And cancerous cells can travel to other parts of the body.
Inherited gene mutations that increase the risk of colon and rectal cancer
In some families, gene mutations passed from parents to children increase the risk of colorectal cancer. These mutations are involved in only a small percentage of rectal cancers. Some genes linked to rectal cancer increase an individual's risk of developing the disease, but they don't make it inevitable.
Two well-defined genetic colorectal cancer syndromes are:
- Hereditary nonpolyposis colorectal cancer (HNPCC). HNPCC, also called Lynch syndrome, increases the risk of colon cancer and other cancers. People with HNPCC tend to develop colon cancer before age 50.
- Familial adenomatous polyposis (FAP). FAP is a rare disorder that causes you to develop thousands of polyps in the lining of your colon and rectum. People with untreated FAP have a greatly increased risk of developing colon or rectal cancer before age 40.
FAP, HNPCC and other, rarer inherited colorectal cancer syndromes can be detected through genetic testing. If you're concerned about your family's history of colon cancer, talk to your doctor about whether your family history suggests you have a risk of these conditions.
The characteristics and lifestyle factors that increase your risk of rectal cancer are the same as those that increase your risk of colon cancer. They include:
- Older age. The great majority of people diagnosed with colon and rectal cancer are older than 50. Colorectal cancer can occur in younger people, but it occurs much less frequently.
- African-American descent. People of African ancestry born in the United States have a greater risk of colorectal cancer than do people of European ancestry.
- A personal history of colorectal cancer or polyps. If you've already had rectal cancer, colon cancer or adenomatous polyps, you have a greater risk of colorectal cancer in the future.
- Inflammatory bowel disease. Chronic inflammatory diseases of the colon and rectum, such as ulcerative colitis and Crohn's disease, increase your risk of colorectal cancer.
- Inherited syndromes that increase colorectal cancer risk. Genetic syndromes passed through generations of your family can increase your risk of colorectal cancer. These syndromes include FAP and HNPCC.
- Family history of colorectal cancer. You're more likely to develop colorectal cancer if you have a parent, sibling or child with the disease. If more than one family member has colon cancer or rectal cancer, your risk is even greater.
- Dietary factors. Colorectal cancer may be associated with a diet low in vegetables and high in red meat, particularly when the meat is charred or well-done.
- A sedentary lifestyle. If you're inactive, you're more likely to develop colorectal cancer. Getting regular physical activity may reduce your risk of colon cancer.
- Diabetes. People with poorly controlled type 2 diabetes and insulin resistance may have an increased risk of colorectal cancer.
- Obesity. People who are obese have an increased risk of colorectal cancer and an increased risk of dying of colon or rectal cancer when compared with people considered normal weight.
- Smoking. People who smoke may have an increased risk of colon cancer.
- Alcohol. Regularly drinking more than three alcoholic beverages a week may increase your risk of colorectal cancer.
- Radiation therapy for previous cancer. Radiation therapy directed at the abdomen to treat previous cancers may increase the risk of colorectal cancer.
Talk to your doctor about when you should start getting screened for colorectal cancer. Guidelines generally recommend having your first colorectal cancer screening test at age 50. Your doctor may recommend more-frequent or earlier screening if you have other risk factors, such as a family history of colon or rectal cancer.
The most accurate screening test is a colonoscopy. In this test, a doctor examines the lining of your rectum and large intestine using a long, flexible tube with a tiny video camera at its tip (colonoscope). The colonoscope is inserted in the anus and advanced through the rectum and colon. As the scope's camera moves through the bowel, it sends a video of the rectal and colonic lining to a monitor the doctor sees. If a polyp or suspicious-looking area of tissue is found, the doctor can also take samples of tissue from these areas with instruments inserted in the colonoscope.
Rectal cancer is often diagnosed when a doctor orders tests to find the cause of rectal bleeding or iron deficiency anemia. A colonoscopy is the most accurate of these tests. In a colonoscopy, a doctor uses a thin, flexible, lighted tube with a video camera at its tip (a colonoscope) to view the inside of your colon and rectum.
Sometimes rectal cancer has no noticeable symptoms. People without symptoms may learn they have rectal cancer when they have a screening colonoscopy — that is, a colonoscopy recommended at age 50 for everyone with an average risk of colorectal cancer.
It's usually possible to remove small tissue samples (biopsies) from suspicious-looking areas during a colonoscopy. Laboratory analysis of this tissue helps pin down the diagnosis.
Staging rectal cancer
Once you are diagnosed with rectal cancer, the next step is to determine the cancer's extent (stage). Staging helps guide decisions about the most appropriate treatments for you. The following blood tests and imaging studies are involved in staging rectal cancer:
- Complete blood count (CBC). This test reports the numbers of different types of cells in your blood. A CBC shows whether your red blood cell count is low (anemia), which suggests that a tumor is causing blood loss. A high level of white blood cells is a sign of infection, which is a risk if a rectal tumor grows through the wall of the rectum.
- Carcinoembryonic antigen (CEA). Cancers sometimes produce substances called tumor markers that can be detected in blood. One such marker, carcinoembryonic antigen (CEA), may be higher than normal in people with colorectal cancer. CEA testing is particularly useful in monitoring your response to treatment.
- Chemistry panel. This test measures a number of chemicals in the blood. Abnormal levels of some of these chemicals may suggest that cancer has spread to the liver. High levels of other chemicals may indicate problems with other organs, such as the kidneys.
- CT (computed tomography) scan of the chest. This imaging test helps determine whether rectal cancer has spread to other organs, such as the liver and lungs.
- MRI (magnetic resonance imaging) of the pelvis. An MRI provides a detailed image of the muscles, organs and other tissues surrounding a tumor in the rectum. An MRI also shows the lymph nodes near the rectum and different layers of tissue in the rectal wall.
Rectal cancer stages
Rectal cancers fall into one of five possible stages (stage 0 through stage 4). The stages, in simplified form, are:
- Stage 0. Cancer cells on the surface of the rectal lining (mucosa), sometimes within a polyp
- Stage I. Tumor extending below the rectal mucosa, sometimes penetrating into the rectal wall
- Stage II. Tumor extending into or through the rectal wall, sometimes reaching and growing on or sticking to tissues next to the rectum
- Stage III. Tumor invading lymph nodes next to the rectum, as well as structures and tissues outside the rectal wall
- Stage IV. Tumor spread to a distant organ or lymph nodes distant from the rectum
Staging also involves examining a sample of tissue taken from the tumor (a biopsy) to determine the tumor's grade. Low-grade tumors tend to grow and spread slowly. In contrast, high-grade tumors grow and spread quickly, so they may need more-aggressive treatment.
During a colonoscopy, the doctor inserts a colonoscope into your rectum to check for abnormalities in your entire colon.
Rectal cancer often requires more than one treatment type (modality), an approach known as multimodal therapy. In general, the treatment modalities used in rectal cancer are the same ones used to treat many other types of cancer. They are:
- Surgery to remove the tumor.
- Chemotherapy, usually consisting of two or more drugs that target cancer cells. In people with rectal cancer, chemotherapy is often used along with radiation therapy, either before or after surgery.
- Radiation therapy, which uses high-powered beams, such as X-rays, to kill cancer cells.
Your surgical options depend on a number of factors, including:
- The stage and grade of the cancer
- The location of the tumor in the rectum
- The size of the tumor
- Your age
- Your general health
- Your medical history
- Your preferences after you learn about different procedures
Some of the procedures commonly used to treat rectal cancer are:
Abdominoperineal resection with end colostomy
Abdominoperineal resection (APR) offers the best chance of cure for rectal tumors located extremely close to the anal sphincter. With cancer in this location, the surgeon has to remove both the tumor and the sphincter. Otherwise, it's not possible to take a margin of healthy tissue on all sides of the tumor — and clear or healthy margins reduce the risk that the cancer will return.
After APR, it is no longer possible to pass stool through the anus. An end colostomy connects the end of the colon that was attached to the rectum before APR to a surgical opening (stoma) in the lower abdomen. Stool then passes into a removable pouch placed over the stoma.
This sphincter-sparing procedure may be an option for rectal cancer surgery if the tumor is at least .39 inch (1 centimeter) above the top of the anal sphincter. The surgeon removes the entire rectum and enough of the surrounding tissue to achieve clear margins. Then the remaining end of the colon may be shaped into a pouch that is connected to the colon. Alternatively, the end of the colon may be connected directly to the anus.
Low anterior resection
This procedure, which also leaves the anus intact, may be performed when the tumor is located in the upper part of the rectum. The surgeon removes the tumor and a margin of healthy tissue around it, leaving the lower part of the rectum. The end of the colon is then attached to the remaining section of the rectum.
Local excision takes out the rectal tumor, along with a margin of healthy tissue and the section of rectal wall beneath the tumor. This technique is generally reserved for early, small stage 1 rectal cancers, after a biopsy shows that the tumor is unlikely to spread or recur.
Unlike the other procedures listed, local excision does not include lymph-node removal. Instead, the excised tissue is examined in a laboratory to make sure the tumor doesn't have features that suggest more-advanced cancer than expected. If any of these features are present, a standard operation may be necessary.
People with rectal cancer associated with Crohn's disease, ulcerative colitis or a genetic predisposition to colorectal cancer typically need surgery that is more extensive than are the procedures described here. Chemotherapy is also needed before or after surgery.
Standard treatment for stage II and stage III rectal cancers is typically a combination of chemotherapy and radiation (chemoradiotherapy) given before surgery (preoperatively). This approach is also an option for treating some stage I rectal cancers that have a high risk of recurring.
Benefits of preoperative chemoradiotherapy include:
- Increased response to radiation because of chemotherapy's effect on cancer cells
- Reduced tumor size
- Lowered cancer stage in some cases
- Better chance that surgery will leave the anal area intact (sphincter-sparing surgery)
- Lower risk of cancer recurrence
The usual period between preoperative chemoradiotherapy and surgery is about six weeks. After surgery, most people also have additional chemotherapy to destroy any remaining cancer cells.
Stage IV rectal cancer
Some of the treatments used in stage II and III rectal cancers may also be appropriate for cancers in stage IV. By definition, though, stage IV rectal cancer has spread (metastasized) to a different part of the body, usually the liver.
In some cases, a metastatic tumor may appear in the liver when the primary tumor is still confined mainly to the rectum and nearby lymph nodes. If this happens, your doctor may recommend surgery to remove both the primary tumor and the liver tumor at once.
In other cases, the primary tumor may have spread to organs near the rectum, such as the uterus and ovaries, before liver metastasis appears. Complex surgery and reconstruction of pelvic structures may be possible in these cases as well.
Drugs for stage IV rectal cancer
Chemotherapy may extend life for people with stage IV rectal cancer, as may radiation therapy in some cases. Either treatment may be given after surgery, while chemotherapy is more commonly used before surgery. Chemotherapy or radiation may be used to relieve symptoms in cases where the cancer is too extensive for surgery.
People with stage IV rectal cancer may receive one of three newer FDA-approved drugs in addition to cancer chemotherapy. These drugs, called biologics, target cancer-cell traits that allow tumors to grow. The addition of a biologic drug to standard chemotherapy has been found to improve response to treatment in certain cases of colorectal cancer. Therapy that includes biologics is called targeted therapy.
The FDA-approved biologics used with chemotherapy in first line treatment of stage 4 colorectal cancer are:
- Bevacizumab (Avastin)
- Cetuximab (Erbitux)
- Panitumumab (Vectibix)
Supportive (palliative) care
Palliative care is focused on providing relief from pain and other symptoms of a serious illness. Palliative care specialists work with you, your family and your other doctors to provide an extra layer of support that complements your ongoing care.
An example of palliative care might be surgery to relieve a blockage of the rectum in order to improve your symptoms.
Palliative care is provided by a team of doctors, nurses and other specially trained professionals. Palliative care teams aim to improve the quality of life for people with cancer and their families. This form of care is offered alongside curative or other treatments you may be receiving.
Preparing for an appointment
If your doctor suspects you may have rectal cancer, you'll likely be referred to one or more specialists who treat rectal cancer, including:
- A doctor who treats digestive diseases (gastroenterologist)
- A doctor who treats cancer (oncologist)
- A surgeon specializing in procedures involving the colon and rectum (colorectal surgeon)
- A doctor who uses radiation to treat cancer (radiation oncologist)
Here are some things you can do before you meet with these doctors:
- Find out if there's anything you need to do before your appointment, such as avoid certain foods or medications.
- Make a list of all your medications, including vitamins or supplements.
- Consider taking a family member or friend along to take notes on what your doctors say, so that you can concentrate on listening.
- Write down questions to ask your doctor.
For rectal cancer, here are some questions you may want to ask:
- In what part of the rectum is my cancer located?
- What is the stage of my rectal cancer?
- Has my rectal cancer spread to other parts of my body?
- Will I need more tests?
- What are the treatment options?
- How much does each treatment increase my chances of a cure?
- What are the potential side effects of each treatment?
- How will each treatment affect my daily life?
- Is there one treatment you feel is best for me?
- What would you recommend to a family member or friend in my same situation?
- How much time can I take to make my decision about treatment?
- Should I seek a second opinion?
- Are there any brochures or other printed material that I can take with me? What websites do you recommend?