Both genetic and environmental factors can cause the changes. However, when a person has an uncommon inherited syndrome, changes can occur in months or years.
Anatomy of the colon and rectum
The large intestine is part of the body’s gastrointestinal (GI) tract or digestive system. The colon and rectum make up the large intestine, which plays an important role in the body’s ability to process waste. The colon makes up the first 5 to 6 feet of the large intestine, and the rectum makes up the last 6 inches, ending at the anus.
Colorectal cancer most often begins as a polyp, a non-cancerous growth that may develop on the inner wall of the colon or rectum as people get older. If not treated or removed, a polyp can become a potentially life-threatening cancer. Finding and removing precancerous polyps can prevent colorectal cancer.
Hyperplastic polyps may also develop in the colon and rectum. They are not considered precancerous.
Types of colorectal cancer
Colorectal cancer can begin in either the colon or the rectum. Cancer that begins in the colon is called colon cancer. Cancer that begins in the rectum is called rectal cancer.
Most colon and rectal cancers are a type of tumour called adenocarcinoma, which is cancer of the cells that line the inside tissue of the colon and rectum.
A person with an average risk of colorectal cancer has about a 5% chance of developing colorectal cancer overall. Generally, most colorectal cancers (about 95%) are considered sporadic, meaning the genetic changes develop by chance after a person is born, so there is no risk of passing these genetic changes on to one’s children.
Inherited colorectal cancers are less common (about 5%) and occur when gene mutations, or changes, are passed within a family from 1 generation to the next. Often, the cause of colorectal cancer is not known. However, the following factors may raise a person’s risk of developing colorectal cancer:
• Age. The risk of colorectal cancer increases as people get older. The majority of colorectal cancers occur in people older than 50.
For colon cancer, the average age at the time of diagnosis for men is 68 and for women is 72.
For rectal cancer, it is age 63 for both men and women. Older adults who are diagnosed with colorectal cancer face unique challenges, specifically with regard to cancer treatment.
• Race. Black people have the highest rates of sporadic, or non-hereditary, colorectal cancer in the United States. Colorectal cancer is also a leading cause of cancer-related death among Black people.
• Gender. Men have a slightly higher risk of developing colorectal cancer than women.
• Family history of colorectal cancer. Colorectal cancer may run in the family if first-degree relatives (parents, brothers, sisters, children) or many other family members (grandparents, aunts, uncles, nieces, nephews, grandchildren, cousins) have had colorectal cancer. This is especially true when family members are diagnosed with colorectal cancer before age 60.
If a person has a family history of colorectal cancer, their risk of developing the disease is nearly double. The risk further increases if other close relatives have also developed colorectal cancer or if a first-degree relative was diagnosed at a younger age.
• Rare inherited conditions. Members of families with certain uncommon inherited conditions have a higher risk of colorectal cancer, as well as other types of cancer.
• Inflammatory bowel disease (IBD). People with IBD, such as ulcerative colitis or Crohn’s disease, may develop chronic inflammation of the large intestine. This increases the risk of colorectal cancer. IBD is not the same as irritable bowel syndrome (IBS). IBS does not increase your risk of colorectal cancer.
• Adenomatous polyps (adenomas). Polyps are not cancer, but some types of polyps called adenomas can develop into colorectal cancer over time. Polyps can often be completely removed using a tool during a colonoscopy, a test in which a doctor looks into the colon using a lighted tube after the patient has been sedated. Polyp removal can prevent colorectal cancer.
• Personal history of certain types of cancer. People with a personal history of colorectal cancer previously, or a diagnosis of ovarian cancer or uterine cancer are more likely to develop colorectal cancer.
• Physical inactivity and obesity. People who lead an inactive lifestyle, meaning no regular exercise and a lot of sitting, and people who are overweight or obese may have an increased risk of colorectal cancer.
• Food/diet. Current research consistently links eating more red meat and processed meat to a higher risk of the disease.
• Smoking. Recent studies have shown that smokers are more likely to die from colorectal cancer than non-smokers.
Different factors cause different types of cancer. Although there is no proven way to completely prevent colorectal cancer, you may be able to lower your risk.
Polyp removal during a colonoscopy can help prevent colorectal cancer.
The following may also lower a person’s risk of colorectal cancer:
• Aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs). Some studies suggest that aspirin and other NSAIDs may reduce the development of polyps in people with a history of colorectal cancer or polyps.
Taking aspirin or other NSAIDs is not a substitute for having regular colorectal cancer screenings.
• Food choices and supplements. A diet rich in fruits and vegetables and low in red meat may help reduce the risk of colorectal cancer.
Some studies have also found that people who take calcium and vitamin D supplements have a lower risk of colorectal cancer.
Screening for colorectal cancer
Colorectal cancer can often be prevented through regular screening, which can find polyps before they become cancerous. People with an average risk should begin screening at age 45.
Because colorectal cancer usually does not cause symptoms until the disease is advanced, it is important for people to talk with their doctor about the pros and cons of each screening test and how often each test should be given.
Under the guidelines below, people should begin colorectal cancer screening earlier and/or undergo screening more often if they have any of the following risk factors for colorectal cancer:
• A personal history of colorectal cancer or adenomatous polyps
• A strong family history of colorectal cancer or polyps, such as cancer or polyps in a first-degree relative younger than 60 or in 2 first-degree relatives of any age. A first-degree relative is defined as a parent, sibling, or child.
• A personal history of chronic IBD
• A family history of any hereditary colorectal cancer syndrome, such as FAP, Lynch syndrome, or other syndromes
The tests used to screen for colorectal cancer are described below.
• Colonoscopy. Allows the doctor to look inside the entire rectum and colon while a patient is sedated. A flexible, lighted tube called a colonoscope is inserted into the rectum and the entire colon to look for polyps or cancer.
• Computed tomography (CT or CAT) colonography. CT colonography, sometimes called virtual colonoscopy, is a screening method being studied in some centers. CT colonography may be an alternative for people who cannot have a standard colonoscopy.
• Sigmoidoscopy. A sigmoidoscopy uses a flexible, lighted tube that is inserted into the rectum and lower colon to check for polyps, cancer, and other abnormalities.
• Fecal occult blood test (FOBT) and fecal immunochemical test (FIT). A fecal occult blood test is used to find blood in the feces, or stool, which can be a sign of polyps or cancer. A positive test, meaning that blood is found in the feces, can be from causes other than a colon polyp or cancer, including bleeding in the stomach or upper GI tract and even eating rare meat or other foods.
• Double contrast barium enema (DCBE). For patients who cannot have a colonoscopy, an enema containing barium is given, which helps make the colon and rectum stand out on x-rays. A series of x-rays is then taken of the colon and rectum.
• Stool DNA tests. This test analyzes the DNA from a person’s stool sample to look for cancer. It uses changes in the DNA that occur in polyps and cancers to find out if a colonoscopy should be done.
Different organizations have made different recommendations for colorectal cancer screening. There are 2 sets of recommendations described below.
The American Society of Clinical Oncology (ASCO) has developed guidelines for colorectal cancer screening to help prevent cancer for people with an average risk. Beginning at age 50, both men and women with an average risk of colorectal cancer should follow 1 of these testing schedules.
The following tests detect both polyps and cancer:
• Flexible sigmoidoscopy, every 5 years or every 10 years with FIT or FOBT every year
• Colonoscopy, every 10 years
• DCBE, every 5 years
• CT colonography, as often as your doctor recommends
These tests primarily detect cancer:
• Guaiac-based FOBT, every year
• FIT, every year
• Stool DNA test, as often as your doctor recommends
Colorectal Cancer: Symptoms and Signs
People with colorectal cancer may experience the following symptoms or signs:
• Diarrhea, constipation, or feeling that the bowel does not empty completely
• Bright red or very dark blood in the stool
• Stools that look narrower or thinner than normal
• Discomfort in the abdomen, including frequent gas pains, bloating, fullness, and cramps
• Weight loss with no known explanation
• Constant tiredness or fatigue
• Unexplained iron-deficiency anemia, which is a low number of red blood cells
Talk with your doctor if any of these symptoms last for several weeks or become more severe.
Because colorectal cancer can occur in people younger than the recommended screening age and in older people between screenings, anyone at any age who experiences these symptoms should visit a doctor to find out if they should have a colonoscopy.
Colorectal Cancer: Types of Treatment
Surgery is the removal of the tumor and some surrounding healthy tissue during an operation. It is often called surgical resection. This is the most common treatment for colorectal cancer. Part of the healthy colon or rectum and nearby lymph nodes will also be removed.
A surgical oncologist is a doctor who specializes in treating cancer using surgery. A colorectal surgeon is a doctor who has received additional training to treat diseases of the colon, rectum, and anus.
In addition to surgical resection, surgical options for colorectal cancer include:
• Laparoscopic surgery. With this technique, several viewing scopes are passed into the abdomen while a patient is under anesthesia. The incisions are smaller and the recovery time is often shorter than with standard colon surgery.
• Colostomy for rectal cancer. This is a surgical opening, or stoma, through which the colon is connected to the abdominal surface to provide a pathway for waste to exit the body. Sometimes, the colostomy is only temporary to allow the rectum to heal, but it may be permanent.
• Radiofrequency ablation (RFA) or cryoablation. Some patients may have surgery on the liver or lungs to remove tumors that have spread to those organs. Using energy in the form of radiofrequency waves to heat the tumors, called RFA, or to freeze the tumor, called cryoablation.
Radiation therapy is the use of high-energy x-rays to destroy cancer cells. It is commonly used for treating rectal cancer because this kind of tumor tends to recur near where it originally started. A doctor who specializes in giving radiation therapy to treat cancer is called a radiation oncologist.
A radiation therapy regimen, or schedule, usually consists of a specific number of treatments given over a set period of time.
External-beam radiation therapy. External-beam radiation therapy uses a machine to deliver x-rays to where the cancer is located. Radiation treatment is usually given 5 days a week for several weeks.
Stereotactic radiation therapy. Stereotactic radiation therapy is a type of external-beam radiation therapy that may be used if a tumor has spread to the liver or lungs. This type of radiation therapy delivers a large, precise radiation dose to a small area. This technique can help save parts of the liver and lung tissue that might otherwise have to be removed during surgery.
Other types of radiation therapy. For some people, specialized radiation therapy techniques, such as intraoperative radiation therapy or brachytherapy, may help get rid of small areas of cancer that can not be removed with surgery.
• Intraoperative radiation therapy. Intraoperative radiation therapy uses a single, high dose of radiation therapy given during surgery.
• Brachytherapy. Radioactive “seeds” placed inside the body. Limited information is available about how effective this approach is, but some studies suggest that it may help slow the growth of cancer cells.
Radiation therapy for rectal cancer. For rectal cancer, radiation therapy may be used before surgery, called neoadjuvant therapy, to shrink the tumor so that it is easier to remove.
It may also be used after surgery to destroy any remaining cancer cells. Both approaches have worked to treat this disease. Chemotherapy is often given at the same time as radiation therapy, called chemoradiation therapy, to increase the effectiveness of the radiation therapy.
Chemoradiation therapy is often used in rectal cancer before surgery to avoid colostomy or reduce the chance that the cancer will recur. The main benefits included a lower rate of the cancer coming back in the area where it started, fewer patients who needed permanent colostomies, and fewer problems with scarring of the bowel where the radiation therapy was given.
A newer approach to rectal cancer is currently being used for certain people. It is called total neoadjuvant therapy (or TNT). With TNT, both chemotherapy and chemoradiation therapy are given for about 6 months before surgery.
Therapies using medication
Treatments using medication are used to destroy cancer cells. Medication may be given through the bloodstream to reach cancer cells throughout the body. When a drug is given this way, it is called systemic therapy. Medication may also be given locally, which is when the medication is applied directly to the cancer or kept in a single part of the body.
This type of medication is generally prescribed by a medical oncologist, a doctor who specializes in treating cancer with medication.
Medications are often given through an intravenous (IV) tube placed into a vein using a needle or as a pill or capsule that is swallowed (orally). If you are given oral medications, be sure to ask your health care team about how to safely store and handle it.
The types of medications used for colorectal cancer include:
• Targeted therapy
A person may receive 1 type of medication at a time or a combination of medications given at the same time. They can also be given as part of a treatment plan that includes surgery and/or radiation therapy.
Chemotherapy is the use of drugs to destroy cancer cells, usually by keeping the cancer cells from growing, dividing, and making more cells.
A chemotherapy regimen, or schedule, usually consists of a specific number of cycles given over a set period of time. A patient may receive 1 drug at a time or a combination of different drugs given at the same time.
Chemotherapy may be given after surgery to eliminate any remaining cancer cells. For some people with rectal cancer, the doctor will give chemotherapy and radiation therapy before surgery to reduce the size of a rectal tumor and reduce the chance of the cancer returning.
Targeted therapy is a treatment that targets the cancer’s specific genes, proteins, or the tissue environment that contributes to cancer growth and survival. This type of treatment blocks the growth and spread of cancer cells and limits damage to healthy cells.
Not all tumors have the same targets. To find the most effective treatment, your doctor may run tests to identify the genes, proteins, and other factors in your tumor. This helps doctors better match each patient with the most effective treatment whenever possible.
Studies have shown that older patients are able to benefit from targeted therapies, similar to younger patients. In addition, the expected side effects are usually manageable in both older and younger patients.
For colorectal cancer, the following targeted therapies may be options.
– Anti-angiogenesis therapy. It is focused on stopping angiogenesis, which is the process of making new blood vessels. Because a tumor needs the nutrients delivered by blood vessels to grow and spread, the goal of anti-angiogenesis therapies is to “starve” the tumor.
– Epidermal growth factor receptor (EGFR) inhibitors. Researchers have found that drugs that block EGFR may be effective for stopping or slowing the growth of colorectal cancer.
– Combined targeted therapies. Some tumors have a specific mutation, called BRAF V600E, that can be detected by an FDA-approved test. A class of targeted treatments called BRAF inhibitors can be used to treat tumors with this mutation.
Immunotherapy, also called biologic therapy, is designed to boost the body’s natural defenses to fight the cancer. It uses materials made either by the body or in a laboratory to improve, target, or restore immune system function.
Physical, emotional, and social effects of cancer
Cancer and its treatment cause physical symptoms and side effects, as well as emotional, social, and financial effects. Managing all of these effects is called palliative care or supportive care.
Palliative care focuses on improving how you feel during treatment by managing symptoms and supporting patients and their families with other, non-medical needs. Any person, regardless of age or type and stage of cancer, may receive this type of care. And it often works best when it is started right after a cancer diagnosis. People who receive palliative care along with treatment for the cancer often have less severe symptoms, better quality of life, and report that they are more satisfied with treatment.
Palliative treatments vary widely and often include medication, nutritional changes, relaxation techniques, emotional and spiritual support, and other therapies. You may also receive palliative treatments similar to those meant to get rid of the cancer, such as chemotherapy, surgery, or radiation therapy.