Screening for Colorectal Cancer: What are the Options?

Colonoscopies are effective, but other screening options are available.

If caught early, colorectal cancer is highly treatable. The key is screening.

“Regular screenings are so important in detecting colorectal cancer or precancerous lesions early in the disease process,” says Joshua Obuch, MD, Geisinger gastroenterologist and director of endoscopy at Geisinger Wyoming Valley Medical Center. “There are several options available for screening, each with its own pros and cons.”

What is colorectal cancer, and what causes it?

Colorectal cancer, also known as colon cancer or bowel cancer, affects the large intestine (colon) and the rectum. The colon is the last part of the digestive system. After food has broken down and nutrients are absorbed, the colon is responsible mostly for absorbing water and creating solid waste. The rectum is the final section of the colon, where stool is stored before it’s passed out of the body.

Colorectal cancer develops when abnormal cells in the colon or rectum grow out of control and form a tumor. If left untreated, colorectal cancer can spread to other parts of the body and be potentially fatal.

Risk factors for colorectal cancer include age, family history, personal history of certain conditions (e.g., inflammatory bowel disease), lifestyle choices (e.g., diet, smoking), and race/ethnicity. While some of these factors can’t be changed, others can be managed by making healthy lifestyle choices and getting regular screenings.

Types and symptoms of colorectal cancer

The most common type of colorectal cancer is adenocarcinoma, which begins in the cells lining the colon or rectum. Other less common types include squamous cell carcinoma, mucinous adenocarcinoma and signet ring cell carcinoma. Often, colon cancer doesn’t have symptoms until it’s become very advanced. When symptoms of colorectal cancer are present, they can vary depending on the location and stage of the tumor. Some common symptoms include:

Blood in the stool or rectal bleeding
A change in bowel habits, such as diarrhea or constipation
Abdominal pain or cramping
Weakness and fatigue
Unexplained weight loss

If you have any of these symptoms, it's important to see your doctor for a diagnosis.

Colorectal cancer screening

For the general population at average risk for colon cancer, several screening options are available.

Colonoscopies

The standard option is a colonoscopy. A doctor inserts a long, flexible tube with a camera into the rectum and colon to look for any abnormal growths or polyps. A colonoscopy can also be used to take biopsies of tissue for further testing or even remove small growths completely before they become a bigger problem. For patients at increased risk for colon cancer, this is the recommended test.

Prior to testing, your bowels must be completely empty to make sure the colon and digestive tract can be seen clearly. To achieve this, patients take a large dose of laxatives.

“While some feel the colon prep can be unpleasant, a complete prep is one of the most important aspects of a high-quality colonoscopy in order to detect and prevent colorectal cancer,” says Dr. Obuch.

Flexible sigmoidoscopies

Another option for screening is a flexible sigmoidoscopy every five years along with annual stool testing (fecal immunohistochemical or FIT testing). A flexible sigmoidoscopy is like a colonoscopy, but only evaluates the last 30% of colonic mucosa, an area where colonic growths tend to form more commonly.

This requires a less intense bowel prep but is not as comprehensive as a colonoscopy. If patients have a positive FIT test, a full colonoscopy is usually recommended.

“A flexible sigmoidoscopy is used to screen for several GI-related conditions, like ulcerative colitis, and it can detect polyps,” says Dr. Obuch. “Its detection abilities for colorectal cancer are limited, so we generally recommend a colonoscopy if we suspect colorectal cancer.”

Stool testing

A third option is stool-based testing. These tests can be done at home and involves collecting a stool sample that will be tested for blood or abnormal DNA. If blood or abnormal DNA are found, you’ll need to have a colonoscopy to confirm the results and to determine the cause.

There are three types of stool-based tests:

A fecal immunochemical test (FIT) is used to detect blood that can’t be seen by the naked eye. It’s also helpful to detect bleeding in the digestive tract when there aren’t other telltale symptoms of illness.
Fecal occult testing (FOBT) is also used to detect blood in your stool, but to do this, it requires you to follow a specific diet (abstaining from red meat and certain medications) prior to submitting a sample. You also have to provide more than one sample for FOBT.
A stool DNA test checks for trace amounts of blood in your stool and can detect DNA changes found in cancerous and precancerous cells.

Virtual colonoscopies

A CT colonography, or virtual colonoscopy, is another option to screen for colorectal cancer. However, if colonic abnormalities are identified you’ll need a colonoscopy to confirm results.

No matter which screening option you prefer, talk to your doctor about your risk factors for colorectal cancer and which option is right for you.