What Is Colorectal Cancer?

Colorectal cancer may begin in either the colon (large intestine) or the rectum. Cancer is caused by malignant (cancerous) cells that grow and multiply without control. These growths, called polyps, may start noncancerous, but can turn into cancer over time. When cancer begins in the tissues of the colon, it is called colon cancer. When it forms in the tissues of the rectum, it is called rectal cancer. Because colon cancer and rectal cancer have many features in common, they are sometimes referred to together as colorectal cancer.

Making up 95% of colorectal cancer, adenocarcinoma is the most common form and often starts as polyps in the cells lining the large intestine. Doctors can screen for polyps during a colonoscopy and may remove them before they turn into cancer.

How Common Is Colorectal Cancer?

Each year, an estimated 150,000 new cases of colorectal cancer in U.S. adults is diagnosed. With about 50,000 deaths from colorectal cancer annually in the U.S., it is the second-leading cause of cancer death in both men and women. Colorectal cancer is the third-most diagnosed form of cancer for both men and women worldwide. The death rate for colorectal cancer has dropped annually, largely attributed to early screening practices finding and removing polyps before they turn cancerous.

How Does Colorectal Cancer Start?

When cells on the inner lining of the colon or rectum grow abnormally, they can produce polyps. While natural for cells to grow, divide and die to keep the body functioning properly, polyps may continue multiplying abnormally and develop cancerous cells. It may take multiple years for a polyp to become cancerous and not all polyps do so. Symptoms of colon cancer from polyps generally do not occur until they've become large or cancerous, so screening to remove polyps at an early stage, before signs of colon cancer appear, can help prevent the growth of cancerous polyps.

Colorectal Cancer Risk Factors

The risk of colorectal cancer increases with age, but a mix of other health conditions and lifestyle influences can impact colorectal cancer risk factors:

  • A family history of colorectal cancer
  • Inflammatory bowel diseases such as Crohn's disease or ulcerative colitis
  • Age over 50
  • A high-fat diet or a diet low in fruits and vegetables
  • Obesity or being overweight
  • Alcohol and tobacco use

Is Colorectal Cancer Hereditary?

The majority of colorectal cancer cases are not tied to a family history of the cancer. Still, up to 30% of all colorectal cancer diagnoses come in families with a history of the cancer.

Colorectal Cancer Symptoms

Colorectal cancer signs and colon cancer symptoms will present themselves differently in patients. Often those with colon cancer do not notice symptoms in the cancer's early stages and when they do show, the colorectal cancer signs vary based on the cancer's size and location within the colon or rectum.

Colon cancer symptoms may include:

  • Abdominal pain
  • Rectal pain or bleeding
  • Change in bowel habits
  • Bloody or black, sticky bowel movements
  • Weight loss for no clear reason
  • Fatigue from anemia (low blood count)
  • Nausea and vomiting
  • Swelling of the abdomen

Rectal cancer symptoms may include:

  • Rectal pain or bleeding
  • Change in bowel habits (for example, going more often)
  • Bloody bowel movements
  • A feeling of not being done after a bowel movement
  • Weight loss for no clear or deliberate reason
  • Fatigue from anemia
  • Rectal or anal pain

The symptoms of colorectal cancer may look similar to those associated with other medical conditions. Please consult your doctor if you notice any of the above symptoms.

Colorectal Cancer Screening

Screening for colorectal cancer means testing for something abnormal before it gives you symptoms. This allows colon cancer or rectal cancer to be found earlier. The sooner colorectal cancer is found, even before colorectal cancer signs appear, the smaller—and more treatable—it is likely to be.

Tests commonly used to screen for colorectal cancer include:

  • Colonoscopy: During a colonoscopy procedure, a long, flexible tube called a colonoscope is inserted through the rectum. It is used to examine the entire rectum and colon for cancer. If anything looks abnormal, the doctor can use the colonoscope to take a biopsy (small tissue sample) for further testing. A colonoscopy is considered the most effective technique to screen patients ages 50 to 75 for colorectal cancer
  • Flexible sigmoidoscopy: During this procedure, a sigmoidoscope (a device similar to a colonoscope) is used to examine the rectum and lower part of the colon
  • Fecal occult blood test: This test checks for occult (hidden) blood in the stool. It involves placing a very small amount of stool on a set of cards, which is then sent to a laboratory for analysis
  • Barium enema with air contrast: Barium (a liquid used to coat the inside of the colon or rectum so they will show up on an X-ray) is given into the rectum to partially fill up the colon. Air is pumped in to expand the colon and rectum. An X-ray of the abdomen is then taken and can show narrowed areas, blockages and other problems

Diagnosing Colorectal Cancer

The first step in diagnosing any disease is to complete a medical history and physical examination. If necessary, more tests and procedures are used to find and diagnose colorectal cancer. (As outlined above, several of these are also used for screening purposes.)

  • Colonoscopy
  • Flexible sigmoidoscopy
  • Fecal occult blood test
  • Barium enema with air contrast
  • Digital rectal examination: A doctor or other health care provider inserts a gloved and lubricated finger into the rectum to feel for anything unusual or abnormal. This test can detect some cancers of the rectum, but not the colon
  • Biopsy: During a colonoscopy or surgery, polyps or tissue samples are removed for examination under a microscope to look for cancer or other abnormal cells
  • Blood count: This test checks for anemia, which can be a result of bleeding from a tumor
  • Imaging tests: Tests such as a computed tomography (CT) scan, positron emission tomography (PET) scan, ultrasound or magnetic resonance imaging (MRI) of the abdomen may be done to look for tumors or other problems

Staging Colorectal Cancer

Following a diagnosis of colorectal cancer, further tests are done to determine the location or density of cancer cells. This process, known as staging, helps your doctor choose the best treatment for you. Imaging tests, surgery and X-rays are common approaches for staging colorectal cancer.

Stages of colorectal cancer range from Stage I (early-stage cancer) to Stage IV (cancer is advanced and has spread to other parts of the body, or metastatic colorectal cancer).

Colorectal Cancer Treatment

Your care team will work with you to develop a treatment plan that is right for you. This plan will depend on many factors, including type and stage of colorectal cancer, your general health, and your treatment preferences.

Treatment may involve one or more of these options:

  • Colorectal surgery is the primary treatment option for colorectal cancer. Surgery—which may be traditional (open) or minimally invasive—involves removal of the cancer, a strip of normal tissue on either side of the cancer and nearby lymph nodes. Minimally invasive approaches include natural orifice endoscopic surgery and sphincter-sparing rectal cancer surgery
  • Radiation therapy uses high-energy radiation beams to kill or shrink tumors while sparing healthy tissue. Forms of radiation therapy to treat colorectal cancer include:
    • External radiation (external beam therapy) - a treatment that precisely sends high levels of radiation directly to the cancer cells
    • Intraoperative radiation therapy - in which radiation is given inside the body as close to the cancer as possible. In some cases, external radiation therapies are used along with this treatment
    • Proton beam radiation – a precise form of radiation therapy designed to target tumors while helping to preserve surrounding healthy tissue
  • Chemotherapy kills cancer cells through the use of intravenous or oral drugs. Studies have shown that chemotherapy after surgery may increase the survival rate for patients with some stages of colon cancer. It can also be helpful before or after surgery for some stages of rectal cancer. Chemotherapy can also help slow the growth or relieve the symptoms of advanced colorectal cancer
  • Targeted therapy refers to a new generation of "smart" drugs that target and interfere with the activity of specific proteins that drive tumor growth and spread
  • Clinical trials, which are available through some hospitals, may provide access to new and promising therapies for colorectal cancer

Colorectal Cancer Prevention

Colorectal cancer prevention should center around both screenings and reducing risk factors within your control. Colorectal cancer screening is one of the most effective ways to catch polyps before they turn cancerous or when the cancerous cells are small and easier to treat. Lifestyle factors, such as eating healthy, staying at a healthy weight, eliminating alcohol and smoking and increasing exercise can all help to reduce the risk of colorectal cancer.

Colorectal Cancer FAQs

What Are the Most Common Types of Colorectal Cancer?

Adenocarcinoma of the colon makes up 95% of all colorectal cancer, the most common form. Adenocarcinoma starts in the cells lining the large intestine as a polyp. Other colorectal cancer types include colorectal carcinoma, carcinoid tumors, gastrointestinal stromal tumors, colorectal lymphoma along with hereditary nonpolyposis colorectal cancer and familial adenomatous polyposis.

Is Colorectal Cancer the Same as Colon Cancer?

Colorectal cancer can mean cancer of either the colon or the rectum, so colorectal cancer and colon cancer are effectively the same.

What Are the First Signs of Having Colon Cancer?

Early stages of colorectal cancer don't always produce symptoms. The early colon cancer signs and symptoms may include abdominal pain, rectal pain or bleeding, change in bowel habits, bloody, black or sticky bowel movements, weight loss for no apparent reason, nausea and vomiting or swelling of the abdomen.

Is Colorectal Cancer Curable?

Colorectal cancers are commonly treated and cured when the cancer remains in the colon or rectum. Surgery has proven successful in eliminating the cancerous cells, although recurrence is common for colorectal cancer.

Does Colon Cancer Cause Back Pain?

It is not uncommon for pain from the cancer site within the colon or rectum to present as lower back pain. Typically, though, back pain accompanies other symptoms of colorectum cancer.

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Video: What is Colorectal Cancer?

Learn more about colorectal cancer and meet Aparna Parikh, MD, medical director of the Center for Young Adult Colorectal Cancer at Mass General Cancer Center, who details why colorectal cancer is being increasingly diagnosed in younger patients around the world.