Description
The term “colorectal cancer” refers to cancers that occur in the lower part of the digestive system – primarily in the colon or rectum. The body’s solid waste is stored in the colon; the rectum is the end of the colon adjacent to the anus. Together, the colon and rectum form the large intestine, a long, muscular tube.
Tumors of the colon and rectum are growths that form on the inner wall of the large intestine. Benign tumors are called polyps. A polyp may look like a wart when it is small, and when it grows it may resemble a cherry on a stem.
Polyps of the colon and rectum almost always are benign. Usually they produce no symptoms, although they may cause painless rectal bleeding or bleeding that cannot be seen by the naked eye. Polyps of the large intestine routinely are removed surgically, and are not life threatening.
If benign polyps are not removed from the large intestine, they can become malignant over time. Most cancers of the large intestine are believed to develop from polyps. Colorectal cancer can invade and damage nearby tissues and organs. Cancer cells also can break away and spread to other parts of the body, such as the liver and lungs, where new tumors form. The spread of cancer from its point of origin to distant organs is called metastasis. Once metastasis has occurred in colorectal cancer, a complete cure of the cancer is unlikely.
Statistics
Colorectal cancer is a relatively common cancer, ranking second in the United States. In 2005, approximately 145,290 new cases of colorectal cancer (71,820 men and 73,470 women) will be diagnosed in the United States. Researchers estimate that more than 56,000 people will die from the disease; slightly more men than women, accounting for ten percent of all cancer deaths in 2005. Blacks in America have the highest rate of incidence; Hispanics have the lowest rates. The cumulative lifetime risk for the disease is one in 20.
Colorectal cancer is extremely curable when caught early. As the disease progresses, survivability rates slide downward.
Early Detection and Diagnosis
Today’s early detection strategies mean that health professionals are catching colorectal cancers in their very early stages, when they are highly treatable. A simple screening procedure called a colonoscopy can find polyps before they ever have a chance to become cancerous.
In a colonoscopy, a doctor inserts a lighted tube into the rectum and colon to look for polyps or other changes such as inflammation or bleeding. Research has shown that removing polyps during a colonoscopy significantly decreases the risk that colorectal cancer will develop.
In many cases, colorectal cancers occur without symptoms, making colonoscopy the best way to check for early signs of colorectal cancer. In addition, there are some warning signs to watch for, including very dark or bright red blood in the stool; unexplained weight loss; persistent exhaustion; changes in the shape, frequency, and consistency of stools; or pain, cramps or bloated feelings in the stomach.
Other commonly used detection methods include a digital rectal exam to feel for any abnormalities by hand, a test to examine the stool for traces of blood, or an X-ray.
Advances in screening technology, and publicizing the importance of routine screenings, have helped to reduce significantly the number of deaths from colorectal cancer.
If signs of cancer are detected using the methods listed above, a doctor will likely take a biopsy – a small tissue sample from the affected area – in order to diagnose definitively or rule out cancer. Polyps removed during a colonoscopy often are biopsied.
Doctors may also use blood tests to look for other common signs of colorectal cancers, such as a high level of a protein called CEA (carcinoembryonic antigen), or an increased number of red blood cells. Neither proves colorectal cancer definitively, however.
If cancer is diagnosed, it is critical for doctors to determine first whether the cancer is limited to the colon or rectum, or if it has begun to metastasize to other areas of the body. This evaluation typically involves using advanced imaging to allow doctors to see a three-dimensional picture of the inside of the body. Any spread of cancer to other organs, such as the lungs or liver, must be discovered or ruled out before an appropriate treatment plan can be created for a patient.
Virtual colonoscopy is being developed as a new way to detect polyps and colon cancer early, without a traditional colonoscopy. This procedure uses a series of X-rays and computer technology to produce images of the colon. It is still being tested to gauge its effectiveness, and is not a standard method of screening at this time.
Minimizing Risk/Prevention
Many uncontrollable factors, such as age, family medical history, or past cancer diagnoses, increase colorectal cancer risk. Age is by far the greatest risk factor. However, there are lifestyle choices one can make to lessen risk.
People who smoke more than 20 cigarettes a day are 250 percent more likely to develop polyps than are nonsmokers who otherwise share the same risk factors (e.g., age, family history). People who drink alcohol have an 87 percent greater likelihood of having polyps compared to nondrinkers. Those who both smoke and drink are 400 percent more likely to develop polyps compared to their peers who neither smoke nor drink. Clearly, avoiding smoking and excessive drinking are critical to preventing colorectal cancer.
Eating a healthy diet also appears to be an important factor in preventing colorectal cancer. Most doctors stress that a diet rich in fruits, vegetables, fiber and legumes can decrease risk. It appears that the phytochemicals in some vegetables have preventive properties. Diets laden with red meat and excessive saturated fat, conversely, seem to increase colorectal cancer risk.
There is increasing evidence that diets high in calcium and folic acid can reduce the risk of colorectal cancer, as well. Research is underway to gather more data supporting this association. Researchers are also studying nonsteroidal anti-inflammatory drugs (NSAIDs) and daily consumption of aspirin to see if these medications can help to prevent colorectal cancer.
Scientists are also improving their understanding of how being overweight and sedentary can contribute to an increased risk of colorectal cancer. So far, evidence shows that maintaining a healthy weight and integrating regular exercise into one’s daily routine can have a measurable positive impact.
Latest Research
Educating the public about the value of screening has helped to reduce death rates from colorectal cancer. On the research front, doctors are developing better drugs and new detection tools as ways to offer patients more accurate screening, improved care and enhanced survivability. In addition, researchers continue to improve their understanding of how genetics and lifestyle choices impact colorectal cancer risk.
One of the most promising developments in colorectal cancer has been the development of new drugs for late-stage colorectal cancer patients. These targeted therapies aim for a specific cell in the body, unlike other forms of chemotherapy which do not discriminate between cancerous and healthy cells. Before the advent of targeted drugs, there were few options for late-stage colorectal cancer patients.
Recently, the U.S. Food and Drug Administration approved two new drugs – Avastin™ (bevacizumab) and Erbitux™ (cetuximab) – which work to keep tumors from getting certain inputs they need in order to grow. Avastin™ blocks blood flow to the tumor, starving it of essential oxygen and nutrients. This landmark concept, called anti-angiogenesis, was first proposed by Dr. Judah Folkman of Harvard University. The mode of action of Erbitux™ is to interfere with cellular signals that encourage tumors to grow. Doctors now (August 2005) have six drugs to use in the fight against advanced colorectal cancers and, in some cases, to double the survival rate.
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 also is 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.
Current Treatment
Surgery is the frontline treatment for early-stage colorectal cancer – that which has not yet spread. Doctors remove the tumor, and possibly surrounding lymph nodes. In rare cases, patients may need to have a colostomy, in which doctors create a hole in the colon for waste to pass through into a bag, which is worn externally by the patient.
For more advanced cancers that may have metastasized, doctors use surgery, chemotherapy and radiation in various combinations. Sometimes chemotherapy is administered before surgery to shrink the tumor. Chemotherapy and radiation are used to kill any traces of cancer that were not removed surgically.
Treatment for advanced colorectal cancer will involve combinations of multiple treatment approaches, aimed primarily at extending life.
Resources
National Cancer Institute
1-800-4-CANCER
www.cancer.gov
American Cancer Society
1-800-ACS-2345
www.cancer.org
Colon Cancer Alliance
1-877-422-2030
www.ccalliance.org
National Colorectal Cancer Research Alliance
1-213-240-3900
http://www.eifoundation.org/national/nccra/splash/index.html