Colorectal cancer, also known as bowel cancer, colon cancer, or rectal cancer, develops from the colon or rectum, which are parts of the large intestine. It often begins as small, non-cancerous growths called polyps that can become cancerous over time if not addressed. This type of cancer is a common health concern, with an estimated 149,500 new cases diagnosed each year in the United States. Despite its prevalence, colorectal cancer is highly treatable and even preventable when detected early, underscoring the importance of regular screening.
Recognizing Warning Signs
Many individuals with colorectal cancer may not experience symptoms in the early stages, as polyps often do not cause noticeable signs. As the cancer progresses, various symptoms can emerge, prompting a need for medical evaluation. A persistent change in bowel habits, such as new or worsening diarrhea or constipation, lasting more than a few days, can be an indicator.
Rectal bleeding or visible blood in the stool is another symptom that warrants attention. Ongoing abdominal discomfort, including cramps, gas, or pain, along with a feeling that the bowel does not empty completely after a bowel movement, are also potential signs. Unexplained weight loss, weakness, and persistent fatigue may also suggest the presence of colorectal cancer. These symptoms, while potentially caused by other conditions, should prompt a discussion with a healthcare provider.
Who Should Be Screened and When
Screening for colorectal cancer is recommended for individuals at average risk starting at age 45. This age recommendation was lowered from age 50 due to a rise in diagnoses among younger adults. For those in good health with a life expectancy exceeding 10 years, regular screening should continue through age 75.
Certain factors increase an individual’s risk, necessitating earlier or more frequent screening. These include a personal history of colorectal cancer or specific types of polyps, or a family history of colorectal cancer. Individuals with a personal history of inflammatory bowel diseases, such as ulcerative colitis or Crohn’s disease, or certain inherited genetic syndromes, also face a higher risk. In such cases, screening might begin as early as age 40, with more frequent intervals like every 3 to 5 years.
Available Screening Methods
Several methods are available for the early detection of colorectal cancer, each with a distinct approach to identifying abnormalities. Colonoscopy involves a doctor examining the entire large intestine for cancer and polyps using a thin, flexible tube with a camera. During this procedure, any polyps found can be removed, which can prevent them from developing into cancer.
Stool-based tests offer a less invasive screening option by analyzing stool samples for signs of cancer. The Fecal Immunochemical Test (FIT) and guaiac-based Fecal Occult Blood Test (gFOBT) detect blood in the stool. The multi-target stool DNA test (mt-sDNA) looks for altered DNA and/or blood in the stool, as cancer or polyp cells can shed mutated DNA into the stool. These stool tests are performed at home and require regular, often annual or every three years, submission of samples.
Flexible sigmoidoscopy is a visual exam that involves inserting a flexible, lighted tube into the rectum and the lower part of the colon. This allows the doctor to view the rectum and about half of the colon, identifying and potentially removing any abnormal areas. While less comprehensive than a colonoscopy, it provides direct visualization of a significant portion of the large intestine. CT colonography, also known as virtual colonoscopy, uses X-rays and a CT scan to create 2-D or 3-D images of the colon and rectum. This method does not require sedation, but if polyps or abnormalities are detected, a follow-up colonoscopy is typically needed for further investigation or removal.
Interpreting Screening Outcomes
After a colorectal cancer screening test, the results will generally fall into one of three categories: negative, positive, or inconclusive. A negative result means that no signs of cancer or precancerous conditions were detected at the time of the test. Even with a negative result, it is important to adhere to the recommended screening schedule, which for average-risk individuals may involve another test in one to five years depending on the method.
A positive screening outcome indicates that the test detected something that warrants further investigation, such as blood or altered DNA in a stool sample. It is important to understand that a positive result does not automatically mean cancer is present, as other factors can cause such findings. The typical next step after a positive non-invasive test is a diagnostic colonoscopy to thoroughly examine the colon and rectum and determine the source of the positive result.
An inconclusive result means the lab was unable to analyze the sample, perhaps due to insufficient sample size, damage to the sample, or an expired kit. In such cases, the individual will be advised to repeat the test. Adhering to follow-up recommendations, whether for repeat screening or diagnostic procedures like a colonoscopy, is important to ensure that any potential issues are identified and addressed in a timely manner.