Research led by experts at Memorial Sloan Kettering has shown that colorectal cancer screening saves lives. The effort to communicate this important public health message has resulted in a dramatic increase in colorectal cancer screening rates, with more than half of the US population over age 50 being screened.
However, it is a common misconception that all people over age 75 should not be tested. As a result, many might think they should skip it or they may be denied access to screening when it may actually be worthwhile. In fact, approximately 4 million people, or 23 percent of all Americans over age 75, have never been tested.
Colorectal cancer is the second leading cause of cancer death, and at least 40 percent of diagnoses occur in people over 75. “Because older people who have never been screened are at higher risk for the disease than their counterparts who have been tested, the balance between the benefits and harms of screening is in favor of screening,” says MSK biostatistician Ann Zauber.
Dr. Zauber is senior author of two recently published studies that offer guidance on when it’s appropriate to consider or discontinue screening among the elderly. She answers questions about her research below.
Why was it important to evaluate the risks and benefits of colorectal cancer screening in the elderly?
The U.S. Preventive Services Task Force guidelines indicate that routine colorectal cancer screening should occur in people between the ages of 50 and 75. They recommend against routine screening in individuals over age 75 who have had regular screening examinations with consistently negative results from age 50 onward. That decision should be made in consultation with the individual’s primary care provider.
Unfortunately, that message has been misunderstood. Many individuals over age 75 who have never been screened for colorectal cancer are under the impression that screening is not beneficial for them. However, the guidelines did not directly address whether screening is appropriate in the elderly who have never been screened. Our goal was to provide evidence to inform the decision-making process between these individuals and their doctors.
How did you come up with your estimates of the risks and benefits of colorectal cancer screening?
We examined the data from several large clinical and observational studies to come up with a decision analysis based on estimates of risk. We tested our analysis on a hypothetical population we constructed —called a microsimulation model — to be consistent with the US population’s natural history for developing and dying from colorectal cancer.
Several screening interventions were evaluated to determine how well each test detected polyps and interrupted the development of the disease, resulting in clinical benefit.
While our estimates match well with the observed data, they are meant to be a guide and do not replace a conversation between patients and their physicians. That is always most important in any kind of clinical care.
What does your research show?
The findings from the study we published in the June 3 issue of the Annals of Internal Medicine show that there is a strong benefit to having at least one screening test for colorectal cancer if you are over the age of 75 and have never been screened.
We also found that, in general, if people really adhere to screening as recommended, they could get almost comparable benefit for the various screening methods we studied, including flexible sigmoidoscopy with a sensitive fecal occult blood test and colonoscopy — a test used to detect and remove polyps from the colon before they become cancerous. As with any population-based estimate, there may be variables in actual clinical practice, where perfect adherence to the recommended screening schedule for these tests is unlikely.
Our subsequent study published in the July 15 issue of the Annals of Internal Medicine suggests that physicians and patients should consider the individual’s comorbidity level — or other medical problems — and life expectancy before making the decision to screen.
Why are other health conditions an important factor for older people to consider when making the decision to get colorectal cancer screening?
A high level of comorbidity may include living with chronic obstructive pulmonary disease, congestive heart failure, severe liver disease, chronic renal failure, dementia, cirrhosis with chronic hepatitis, or AIDS. As the number and severity of health conditions like these increases, life expectancy is shorter. You don’t want to subject someone with a shorter life expectancy to a test like colonoscopy that has some risk of harm.
Colonoscopy is the most frequently used screening tool today, and while complications from colonoscopy and polyp removal are relatively rare in most people, the elderly have an increased risk of perforations and bleeding from this procedure. Other important considerations include the possibility of false positives and overdiagnosis of cancer; the cardiovascular effects of anesthesia used during the test; and the required bowel preparation, which is crucial in order to get clear views of the colon but has the potential to cause dehydration in some people.
Taking comorbidities and life expectancy into consideration reduces exposure to these risks. Also, if you have a higher risk of dying because of other health issues, you would not likely reap the longer-term preventive benefits of finding and removing precancerous polyps or detecting colon cancer early through screening.
What are the key messages people should know about your research findings?
Our findings support and encourage people over age 75 who have never been screened to have a discussion with their doctor about their individual risks and benefits in order to decide whether colorectal cancer screening is right for them, which test is best suited for that person, and when it’s appropriate to discontinue screening.
There are consequences and costs associated with any kind of screening. We want to ensure that what could be detected and removed with colorectal cancer screening and follow-up is going to benefit the patient. It should result not only in years gained but also in an improvement in the quality of those additional years.