Even over 7 years after a positive FOBT result, only a little over half of older adults received follow-up colonoscopy. Among those who received follow-up colonoscopy, more than a quarter had significant adenomas or cancer detected and treated and lived > 5 years, potentially benefitting from screening, while approximately 59% (70/118) had no significant findings on follow-up and 10% experienced complications from colonoscopy or cancer treatment. Among patients who did not receive follow-up colonoscopy, nearly half died of other causes within 5 years while 4% ultimately died of colorectal cancer. Patients with worst life expectancy (life-expectancy of 5.4 years) were more likely to experience net burden compared to patients with average or best life expectancy. As current guidelines from the USPSTF and other groups encourage individualized decision-making in patients over 75,16,26
our study provides data about the consequences following the choice to pursue or forego follow-up of a positive FOBT result.
The low rate of follow-up colonoscopy found in this study (56%) is similar to that of other studies in older adults even though the follow-up period in other studies ranged from only a few months to 3 years whereas we extended the follow-up period to 7 years.1-4,7,8
Patients may not get follow-up colonoscopy because of the risks of colonoscopy and treatment and other competing causes of mortality, as perceived either by the physician27
or the patient.5
We found that nearly half of those without follow-up colonoscopy died of causes other than colorectal cancer within 5 years, suggesting that the decision to forego follow-up colonoscopy was appropriate for those patients. It also suggests such decisions are occurring after FOBT results are known rather than following recommendations to avoid screening FOBT if there is no intention to follow-up a positive result with colonoscopy. As the use of screening colonoscopy increases, colonoscopy decisions will be made up front and will need to be better targeted than FOBT or the number of colonoscopies performed in people who die within 5 years will increase.
Among our patients with follow-up colonoscopy, about a third had colorectal cancer or significant adenomas, on par with other studies.10,28,29
Strul et al. found the overall adenoma rate in older adults to be 26%.30
Our study indicates that older patients without follow-up had a 4% risk of ultimately dying of colorectal cancer in the next 5 years. On the other hand, undergoing follow-up procedures is not without risk. While prior studies have suggested minimal complications from colonoscopy in older adults, these studies only followed patients over a short period.4,31-35
We found complications of follow-up encompassed more than immediate events. In our cohort, four of the 40 older patients with cancer or significant adenomas were hospitalized for several weeks as a result of complications from treatment. In addition, 23% (24/104) of those with follow up colonoscopy, excluding those with cancer, had 3 or more additional tests over 7 years. However, while older adults are often at greatest risk for complications from colonoscopy and colorectal cancer treatment due to their increasing comorbidity36
, they may be most likely to benefit from screening, especially if they have a substantial life expectancy.
While our study is not a randomized trial, the lengthy follow-up allows us to identify patients who most likely received net benefit from real world screening and follow-up practices, i.e., those with significant disease treated as a result of screening and lived more than 5 years. The choice of a 5 year survival time to achieve benefit is based on the natural history of polyps18
and randomized trials that shows survival benefit begins around 5 years after the start of FOBT screening.10
In addition, several of the cancers and adenomas found in our study were large (>3cm) such that it is reasonable to expect that they would have caused symptoms within 5 years. As with all screening tests, FOBT does not benefit most patients because most do not have cancer or significant adenomas. Yet, more than 15.6% (33/212) of patients aged 70 years and older had colorectal cancer or significant adenomas successfully treated and lived more than 5 years suggesting that a significant minority received net benefit from current practices.
It makes intuitive sense that patients with the best life expectancy are more likely to benefit from screening than those with the worst. This has been shown in cost-effectiveness analyses,37,38
which are based on numerous methodological assumptions, whereas our study uses real world data to describe outcomes of screening according to life expectancy. We found older patients with best predicted life expectancy were less likely to experience net burden from screening than those with the worst. Our study supports guidelines that recommend using life expectancy to guide colorectal cancer screening decisions in older adults and argues against one-size-fits-all interventions that simply aim to increase overall screening and follow-up rates.16,26
We used the well-validated Charlson-Deyo comorbidity index because it strongly predicts long-term mortality.14
In our cohort it effectively stratified patients into groups with widely differing 5-year mortality rates, ranging from 6% for patients with best life expectancy to 47% for those with worst (life expectancy of 5.4 years) for whom most would not recommend screening.36
However, more comprehensive prognostic indices (e.g. incorporating functional status) over more than 5 years are needed to better guide physicians as they target screening and follow-up to those older adults with substantial life expectancies.39,40
This study has several limitations. First, our cohort is primarily comprised of men who use the VA, so the generalizability of our findings to non-white men, women and persons not in the VA is uncertain. However, the VA is the largest healthcare system in the U.S. so outcomes of screening and follow-up in this system are likely to have generalizable lessons for US healthcare. Second, our sample size was small because only 212 (9%) patients had positive screening FOBT results at the 4 participating facilities in 2001. Third, although we used Medicare claims data for the first year of follow-up, we relied on chart review for later outcomes which may miss some complications or testing outside the VA, and we were unable to find pathology results for 8 patients with a colonoscopy outside the VA, although all 8 remained alive without colorectal cancer. Fourth, we defined patients as having benefitted from screening if they had colorectal cancer or significant adenomas detected on follow-up colonoscopy and treated AND survived more than five years. Others may argue for a longer or shorter survival length to define benefit in older adults.10,41
In conclusion, systematic reviews of colorectal cancer screening have called for more studies to assess the net benefit of real world colorectal cancer screening practices to improve appropriate use and minimize burdens of screening.39
Our study employed a novel method of following patients with a positive screening FOBT result for 7 years to determine the net benefit and burden of real world screening and follow-up practices in older adults. We demonstrated that older adults with substantial life expectancies are less likely to experience net burden than those with limited life expectancies. Therefore, through individualized decision-making the percentage of patients experiencing net burden could be decreased by better targeting FOBT screening and follow-up to healthy older adults.