Colorectal cancer affects the lining of the large intestine and rectum.
What is going on in the body?
The colon is also called the large intestine. The colon begins near the junction of the small intestine and extends to the rectum.
The colon has four parts:
the cecum and ascending colon, which are in the right side of the abdomen
the transverse colon, which runs across the abdomen and rises slightly as it crosses from the right to the left side
- the descending colon, which drops down along the left side of the abdomen
- the sigmoid colon, a U-shaped bend of bowel that leads from the descending colon toward the rectum
The rectum is below the sigmoid colon, and lies below the level of the peritoneum (the lining of the inside walls of the abdomen).
Colorectal cancer starts in the lining, or mucosa, of the bowel. It usually develops in one area of the bowel over a long period of time. It occurs on the left side in the descending colon 40% to 50% of the time. The cancer generally begins along the interior lining in the colon, then, if not detected, also grows further into the lining and muscle tissue. Like other tumors, colorectal cancer can spread to lymph nodes and other parts of the body.
What are the causes and risks of the disease?
Colorectal cancer is the third most common cancer. People have an increasing risk for it starting at the age of 40. People over the age of 50 account for 93% of colorectal cancer cases.
Experts believe that this slow-growing cancer begins when normal cells in the mucosa become overactive. These overactive cells form a small benign tumor called an adenoma. Abnormal cell changes continue, ultimately turning into cancer. Several genes play a role in colorectal cancer, too.
Some risk factors for the disease are:
- small growths in the colon called colorectal polyps
- polyp syndromes, which means that colorectal polyps form frequently
- a family history of colorectal cancer
- ulcerative colitis, a chronic inflammatory disease of the bowel mucus, or inflammation of the colon that results in ulcers
- environmental factors
Certain foods increase the risk for getting this disease, such as:
- eating a lot of meat
- eating a diet high in fat and low in fiber
What can be done to prevent the disease?
Research findings show that eating a diet high in fiber and getting enough calcium can help prevent colorectal cancer. Use of aspirin and vitamin E are also associated with a lower risk of colorectal cancer.
Early diagnosis is key to preventing death from this disease. Starting at the age of 40, people should have yearly digital rectal exams and fecal occult blood tests. This screening allows early detection of colorectal polyps. These precancerous lesions can be removed before they turn into colorectal cancer.
Beginning at the age of 50, a person should have asigmoidoscopy every 3 to 5 years. A sigmoidoscopy is a procedure that allows a healthcare professional to look into the rectum and the sigmoid colon through a flexible scope.
More frequent or earlier screening may be needed for people who:
- have a family history of colorectal cancer
- have developed colorectal polyps. Polyps are removed during sigmoidoscopy to keep the polyps from becoming cancerous or to assess a person's future risk for cancer.
People who are at high risk for colorectal cancer because of family polyp syndrome or ulcerative colitis often choose to have the colon removed. This is called a colectomy.
Barium enema x-rays are also used for early diagnosis of colorectal polyps.
How is the disease diagnosed?
Colorectal cancer may be diagnosed in several ways, including:
- colonoscopy, a procedure in which a healthcare professional can look into the entire colon and collect tissue samples through the scope
- colon surgery
- endoscopy, a procedure in which a small tube is used to take a sample of tissue
Colorectal cancer is divided into stages, and the likelihood of cure and long-term disease-free survival is determined by the stage.
To determine the stage of the cancer, a surgeon removes the primary tumor and surrounding colon. Local lymph nodes are also removed and the abdomen is explored. The tissue is then examined under a microscope.
The stages of colorectal cancer are:
- Stage A, which is very limited and highly curable
- Stages B1 and B2, in which the cancer has invaded the bowel wall but hasn't spread to any of the lymph nodes
- Stages C1 and C2, in which cancer has invaded the bowel wall and has spread to some of the nearby lymph nodes
- Stage D, in which the cancer has spread to distant sites such as the lung, liver, and lymph nodes
Sometimes, the primary tumor or the sites where the cancer has spread cannot be removed entirely. In these cases, other tests can help in diagnosis, such as:
- CEA tumor marker, a blood test to determine whether the cancer cells have spread to another site
- CT scans of the liver and abdomen
- chest X-ray
Long Term Effects
What are the long-term effects of the disease?
People with Stage D cancer generally cannot be cured. They can survive for several weeks to a few years depending on the tumor's location and behavior. Home healthcare or hospice care may be helpful.
What are the risks to others?
Colorectal cancer is not contagious and poses no risk to others. However, it does tend to run in families.
What are the treatments for the disease?
Several healthcare professionals often work together to help manage colorectal cancer. Among them might be a general surgeon or cancer surgeon, radiation oncologist, medical oncologist, and a primary care physician.
Colorectal cancer is primarily treated with surgery. The surgeon removes the entire tumor, if possible. Often, this means part of the colon must be removed. This is called a hemicolectomy. The colon may be reconnected internally. In this case, the rectal-anal sphincter may be preserved and the person will have normal bowel movements.
In other cases, a colostomy may be needed. A colostomy allows the stool to drain into a bag on the outside of the body. If cancer has spread to the lymph nodes, the risk of a recurrence is higher. Usually, surgery is combined with radiation and chemotherapy.
A person with rectal cancer may be given radiation before, during, or after surgery. The purpose of the radiation is to decrease the risk of tumor recurrence. Often, one or more chemotherapy medications, such as fluorouracil (5-FU), capecitabine (oral 5-FU), leucovorin, oxaliplatin and irinotecan, are given over several months. This significantly reduces the likelihood that cancer will recur several years later.
Sometimes the cancer has spread too far to be removed surgically. While a number of chemotherapy medications are used at this point, none offer a cure. Treatment mostly relieves symptoms, such as swelling and jaundice. Colorectal cancer responds to chemotherapy in less than 50% of cases. Research into treatment options for colon cancer continues, in the hope of producing better response rates than are seen currently.
What are the side effects of the treatments?
Depending on the site and size of the tumor, colostomy can be a side effect of surgery for colorectal cancer. Rectal cancer is treated aggressively with surgery, radiation, and sometimes chemotherapy.
Side effects can include:
- bladder inflammation resulting from radiation
- prostatitis, or inflammation of the prostate
- erectile dysfunction
- pelvic burns
Occasionally, there are other problems, such as:
- poor healing of the colostomy or a portion of the bowel
- poor absorption of food after part or all of the colon is removed
When chemotherapy is given, it is usually tolerated well. However, side effects can include:
- mouth irritation
- low red and white blood cell counts
- painful, reddened, swollen hands or feet
- hair loss
Side effects of treatment for late-stage colorectal cancer vary depending on the medications used but may include those mentioned above. The drawbacks may outweigh the benefits. Sometimes, chemotherapy medications are given directly into an artery that supplies the liver, in order to target tumors that have spread there.
Side effects from this approach include:
- inflammation of the pancreas, called pancreatitis
- blood clots
What happens after treatment for the disease?
After treatment, a person must be watched to make sure that the reconnected bowel or the colostomy is working.
How is the disease monitored?
Monitoring for recurrence of colorectal cancer can involve:
- physical exams
- fecal occult blood test
- lab tests, including tests of the CEA tumor marker
- chest X-ray
- CT scans of the abdomen and pelvis
Colorectal cancer usually does not grow rapidly. Recurrences can happen several years later. Also, a second primary tumor can develop in the remaining bowel.