Description
Cancers of the colon and rectum are caused by out-of-control division and growth of abnormal colon and rectal cells, which cause tumors. Because colon and rectum cancers behave similarly, they are often categorized together as "colorectal cancers," yet treatments vary according to the location of cancer.
The colon and rectum are part of the gastrointestinal ("GI tract"), or digestive tract, the region of the body where food is broken down for energy and nutrients and waste is excreted. After food is digested by the stomach and small intestine, it moves to the colon, a segment of the large intestine, where final nutrients and water are absorbed before passing waste to the rectum, where waste is stored until exiting through the anus.
Most cancers of the large intestine are believed to originate in non-cancerous (benign) tumors, known as polyps or adenomas in the innermost layers of tissue walls of the colon and rectum. If benign adenomas are not removed from the large intestine, they can become malignant (cancerous) and invade outer layers of the colon and rectal walls as well as blood and lymph vessels over time. Once in the lymph or blood vessels, colorectal cancer can quickly spread throughout the body. The spread of cancer from its point of origin to distant organs is called metastasis. The extent of the spread of cancer will influence the type of treatment a patient will receive.
Types of Colorectal Cancers
Most colorectal cancer begins in benign adenomas that are located in the lining of the colon and rectum. Most colorectal cancers are a type of tumor known as an adenocarcinoma, which is a cancer of the glandular cells in the lining of the colon or rectum.
Symptoms
There are few warning signs of the presence of polyps and cancer in the colon and/or rectum. In some cases, patients with colorectal cancers will report the following symptoms:
- Vomiting
- Very dark or bright red blood in stool
- Weight loss
- Changes in shape, frequency and consistency of stools
- Pain, cramps or bloated feelings in stomach
Most often, benign adenomas and colorectal cancers are discovered by an internal examination of the colon and rectum, or colorectal cancer screening.
How Common are Colon and Rectal Cancers?
- Colorectal cancer is one of the most commonly diagnosed cancers in United States.
- In 2008, researchers estimate that approximately 108,070 colon cancers and 40,740 rectum cancers will be diagnosed among U.S. adults.
- Approximately 49,960 people will likely die from colorectal cancer this year.
- Today, there are more than one million colorectal cancer survivors living in the United States.
The number of people dying from colorectal cancer has dramatically declined over the past decade thanks to efforts to promote regular colorectal cancer screening, which detects adenomas and colorectal cancer before cells become cancerous or before the progression of the disease.
Disparities
- African-Americans have highest rates of colorectal cancer
- Despite decreases in rates of colorectal cancer mortality, African-American rates of mortality remain significantly higher than other racial/ethnic groups.
Risk Factors
While researchers have yet to determine the direct cause of colorectal cancers, there are factors that can increase the likelihood of developing colorectal cancer. Personal and family history of disease as well as lifestyle choices can increase an individual's risk of developing colorectal cancer.
Common risk factors for colorectal cancer include:
- History of colorectal adenomas and dysplasia (abnormal cells lining the colon and rectum)
- Personal history of certain types of cancer
- Colorectal, ovarian, endometrium (uterus) and breast cancers increase risk of developing colorectal cancer.
- History of chronic inflammatory bowel disease (IBD)
- Main types of IBD diseases are Crohn's and ulcerative colitis disease
- Chronic inflammation of the large intestine that is characteristic of IBD diseases increases the risk of colorectal cancer
- Family history of colorectal cancer
- Genetic mutations that lead to colorectal cancer syndromes
- Hereditary non-polyposis colorectal cancer (HNPCC), or Lynch syndrome
- Caused by mutation to HNPCC gene
- Individuals with HNPCC mutation typically develop colorectal cancer
- Familial adenomatous polyposis (FAP)
- Caused by mutation to APC gen
- Mutation causes hundreds of adenomas to form in the colon and rectum; if adenomas are not removed, most affected individuals will develop colorectal cancer by 40
- Cigarette smoking increases the risk of developing colorectal adenomas
Diagnosis
The first step to protect against colorectal cancer is to make regular colorectal cancer screenings a priority. Colorectal cancer screenings can identify adenomas before they become cancerous and identify colorectal cancer before symptoms of the disease appear. Doctors recommend that individuals at high risk for developing colorectal cancer and those over the age of 50 receive regular colorectal screenings. Colorectal cancer is extremely curable when caught early. With disease progression, however, survivability rates decline.
Available colorectal screening tests:
- Fecal occult blood test (FOBT): method for detecting invisible traces of blood in stool
- Blood vessels that support polyps or cancerous tumors can be damaged by movement of feces; blood vessel damage causes the release of blood in stool
- Presence of blood alone does not guarantee colorectal adenomas or cancer; further tests will be conducted to determine whether adenomas or cancer are the source of the blood.
- Double-contrast barium enema: method for identifying large colorectal adenomas and cancer by x-ray images of colon and rectum
- Barium solution and air are used to open colon and rectum so that x-ray images can offer clear pictures of potential tumors
- Sigmoidoscopy: method for identifying polyps in rectum and lower section of colon
- Doctor will examine for adenomas by inserting a flexible, lighted tube into the rectum and lower portion of colon
- Colonoscopy: method for identifying colorectal adenomas
- Unlike the sigmoidoscopy, the colonoscopy allows a doctor to examine the rectum and entire colon for adenomas by inserting a lighted tube into the rectum and colon to look for adenomas or other changes such as inflammation or bleeding.
- If a fecal occult blood test, double-contrast barium enema, or sigmoidoscopy indicates the presence of adenomas, a colonoscopy will be performed.
- Potential adenomas identified by colonoscopy will be removed during the colonoscopy.
As part of a routine exam, a doctor will perform a digital rectal exam (DRE). While a DRE can identify abnormal growths in the anal canal and lower portion of the rectum, this method is not meant to stand in place of colorectal screening.
If a doctor suspects a patient to have colorectal cancer, additional blood tests may be performed. Patients with colorectal cancer may show:
- Low red blood counts (also called anemia)
- Tumor markers, or substances released by colorectal cancer into the blood
Typically, after a doctor removes potential adenomas during a biopsy, a piece of tissue will be analyzed by microscopic examination to determine whether or not the lesions are adenomas (precancerous) or malignant (cancerous).
If biopsy indicates the presence of cancer:
- Additional imaging tests such as CT, MRI, ultrasound, chest x-ray, and PET will help to evaluate whether cancer has spread to other regions of the body
- Doctors will assign a cancer type and category, or "stage," based upon the size of tumor, how quickly cancer cells are growing, and whether or not cells have spread into other tissues or other regions of the body; the stage and type of cancer will greatly influence how cancer is treated.
Treatment Options
Surgery
Typically, surgery is the first line of defense against colon and rectal cancers; in some cases, rectal cancer surgery may be preceded by radiation or chemotherapy (to shrink tumor or prevent spread of cancer). Depending upon cancer type and stage, surgery may be more or less invasive, and combined with other therapy.
Types of surgery for removal of colon cancer:
- Polypectomy: very small, early cancers may be removed during colonoscopy
- Laparoscopic surgery: thin, lit tube (laparoscope) is inserted through a small incision in abdomen, which illuminates the suspected cancer region; once cancer is located, doctor removes cancer and surrounding tissue and lymph nodes through abdomen
- Segmental resection: cancer and portion of surrounding colon tissue and lymph nodes are removed through abdomen
Types of surgery for removal of rectal cancer:
- Polypectomy: very small, early cancers may be removed during colonoscopy or sigmoidoscopy
- Local trasanal resection: cancer and surrounding rectal tissue are removed through anus; used for early stage rectal cancer
- Low anterior resection: cancer and surrounding rectal tissue and lymph nodes are removed through abdomen
- Abdiminoperineal (AP) resection: cancer, surrounding rectal tissue, and lymph nodes are removed through abdomen; anus and sphincter tissues are also removed
Chemotherapy
Chemotherapy, or anti-cancer drug treatment, attempts to halt uncontrolled cell division of cancer by destroying all rapidly dividing cells. Different chemotherapy drugs will be prescribed based upon the type and stage of breast cancer.
While doctors may prescribe different types of anti-cancer drugs, chemotherapy can be used to:
- Reduce the risk of recurring colorectal cancer following removal of tumor
- Treat colorectal cancer that has metastasized, or spread, to other regions of the body
Anti-cancer drugs can be taken by mouth or vein. Commonly prescribed chemotherapy drugs for colorectal cancers are:
- Fluorouracil (5-FU)
- Capecitabine (Xeloda®)
- Irinotecan (Camptosar®)
- Oxaliplatin (Eloxatin®)
Although chemotherapy techniques wipe out cancer cells, many normal, rapidly dividing healthy cells are also killed by these treatments. The death of healthy cells causes undesirable side effects for cancer patients such as hair loss, mouth sores, nausea and more. To decrease harmful side effects of chemotherapy, researchers are working to develop ways to tailor anti-cancer drugs to destroy cancer cells alone or interfere with the processes that promote cancer growth. Several drugs that target cancer cells only are listed below:
- Cetuximab (Erbitux®) and Panitumumab (Vectibix®): monoclonal antibodies attack epidermal growth factor receptor (EGFR), which are present on the surface of cancer cells, interfering with cancer cell growth
- Bevacizumab (Avastin®): blocks vascular endothelial growth factors (VEGF), a protein that helps tumors to build blood vessels, disabling tumors from accessing nutrients and oxygen
Radiation
Radiation therapy fights cancer by damaging cancer cells with a powerful blast of energy. While researchers direct radiation at cancer cells, they cannot be fully isolated and radiation often kills normal, healthy cells of the body. New radiation techniques are better able to avoid damaging normal tissue when treating colorectal cancer.
Colorectal cancers are often treated with radiation in the following cases:
- To destroy any cancerous cells that remain after surgery to remove colon or rectal cancers
- To help shrink a colorectal tumor that cannot be removed with surgery; decrease pain associated with advanced stage colorectal cancer
Types of radiation treatments:
- External beam radiation: radiation energy directed from outside source aimed at tumor region
- Most recommended in patients with colon cancer
- Treatment typically lasts several weeks
- Endocavitary radiation therapy: radiation therapy for rectal cancer delivered through device inserted into anus
- Radiation technique aims directly at rectal cancer
- Brachytherapy: internal radiation planted in tissue near rectal cancer
New Scientific Developments
While an increase in the number of regular colorectal screenings have helped to reduce death rates from colorectal cancer over the past decades, researchers continue to search for ways to improve early diagnosis of disease, prognosis and treatment.
In the last few years, researchers have made great strides in understanding genetic risk factors, that is, how people inherit genes related to colorectal cancer. Doctors have identified several genes associated specifically with colorectal cancer risk, such that people known to be at higher risk can be encouraged to seek screening earlier and more often.
Work is also underway to develop methods that leverage the body's own immune system to fight cancer. These "cancer vaccines," trick the immune system to recognize the cancer as foreign, and encourage the body to mount a fight against it.
Finally, doctors are combining several types of drugs and chemotherapies to increase the effectiveness of the overall chemotherapy.
Resources
National Cancer Institute
1-800-4-CANCER
www.cancer.gov
American Cancer Society. Cancer Facts & Figures. Atlanta, American Cancer Society, 2008
1-800-ACS-2345
www.cancer.org
Colon Cancer Alliance
1-877-422-2030
www.ccalliance.org
National Colorectal Cancer Research Alliance
www.eifoundation.org/national/nccra/splash/index.html
Related AACR Press Releases
Cetuximab and Irinotecan Combination Increases Survival in Metastatic Colorectal Cancer, EPIC Trial Researchers Report
April 16, 2007
Cetuximab Increases Survival in Advanced Colorectal Cancer Patients, Studies Show
April 16, 2007
Last reviewed: July 16, 2008