Unrelated Death After Colorectal Cancer Screening: Implications for Improving Colonoscopy Referrals

Discussion

This retrospective analysis followed patients for a mean time of 7 years after a colonoscopy for CRC screening or polyp surveillance. We noted a high rate of all-cause mortality, with 20% of the cohort dying within the period studied. Malignancies, cardiovascular diseases, and advanced lung diseases were most commonly listed causes of death. As expected, CRC was among the 3 most common malignancies and was the cause of death in 6.7% of the group with sufficiently detailed information. While these results fall within the expected range for the mortality related to CRC,⁹ the results do not allow us to assess the impact of screening, which has been shown to decrease cancer-related mortality in veterans.⁶ This was limited because the sample size was too small to assess the impact of screening and the cause of death was ascertained for a small percentage of the sample.

Although our findings are limited to a subset of patients seen in a single center, they suggest the importance of appropriate eligibility criteria for screening tests, as also defined in national guidelines.¹ As a key anchoring point that describes the target population, age contributed to the rate of relatively early death after the index procedure. Consistent with previously published data, we saw a significant impact of comorbid diseases.^10,11 However, our findings go beyond prior reports and show the important impact of psychiatric disease burden, most important the role of SUDs. The predictive value of a summary score, such as the Charlson Comorbidity Index, supports the idea of a cumulative impact, with an increasing disease burden decreasing life expectancy.^10-14 It is important to consider the ongoing impact of such coexisting illnesses. Our analysis shows, the mere history of prior problems did not independently predict survival status in our cohort.

Although age is the key anchoring point that defines the target population for CRC screening programs, the benefit of earlier cancer detection or, in the context of colonoscopy with polypectomy, cancer prevention comes with a delay. Thus, cancer risk, procedural risk, and life expectancy should all be weighed when discussing and deciding on the appropriateness of CRC screening. When we disregard inherited cancer syndromes, CRC is clearly a disease of the second half of life with the incidence increasing with age.¹⁵ However, other disease burdens rise, which may affects the risk of screening and treatment should cancer be found.

Using our understanding of disease development, researchers have introduced the concept of time to benefit or lag time to help decisions about screening strategies. The period defines the likely time for a precursor or early form of cancer potentially detected by screening to manifest as a clinically relevant lesion. This lag time becomes an especially important consideration in screening of older and/or chronically ill adults with life expectancies that may be close to or even less than the time to benefit.¹⁶ Modeling studies suggest that 1,000 flexible sigmoidoscopy screenings are needed to prevent 1 cancer that would manifest about 10 years after the index examination.^17,18 The mean life expectancy of a healthy person aged 75 years exceeds 10 years but drops with comorbidity burden. Consistent with these considerations, an analysis of Medicare claims data concluded that individuals with ≥ 3 significant comorbidities do not derive any benefit from screening colonoscopy.¹⁴ Looking at the impact of comorbidities, mathematical models concluded that colorectal cancer screening should not be continued in persons with moderate or severe comorbid conditions aged 66 years and 72 years, respectively.¹⁹ In contrast, modeling results suggest a benefit of continued screening up to and even above the age of 80 years if persons have an increased cancer risk and if there are no confounding comorbidities.⁴

Life expectancy and time to benefit describe probabilities. Although such probabilities are relevant in public policy decision, providers and patients may struggle with probabilistic thinking when faced with decisions that involve probabilities of individual health care vs population health care. Both are concerned about the seemingly gloomy or pessimistic undertone of discussing life expectancy and the inherent uncertainty of prognostic tools.^20,21 Prior research indicates that this reluctance translates into clinical practice. When faced with vignettes, most clinicians would offer CRC screening to healthy persons aged 80 years with rates falling when the description included a significant comorbid burden; however, more than 40% would still consider screening in octogenarians with poor health.²²

Consistent with these responses to theoretical scenarios, CRC screening of veterans dropped with age but was still continued in persons with significant comorbidity.²³ Large studies of the veteran population suggest that about 10% of veterans aged > 70 years have chronic medical problems that limit their life expectancy to < 5 years; nonetheless, more than 40% of this cohort underwent colonoscopies for CRC screening.^24,25 Interestingly, more illness burden and more clinical encounters translated into more screening examinations in older sick veterans compared with that of the cohort of healthier older persons, suggesting an impact of clinical reminders and the key role of age as the main anchoring variable.²³

Ongoing screening despite limited or even no benefit is not unique to CRC. Using validated tools, Pollock and colleagues showed comparable screening rates for breast and prostate cancer when they examined cohorts at either high or low risk of early mortality.²⁶ Similar results have been reported in veterans with about one-third of elderly males with poor life expectancy still undergoing prostate cancer screening.²⁷ Interestingly, inappropriate screening is more common in nonacademic centers and influenced by provider characteristics: nurse practitioner, physician assistants, older attending physicians and male physicians were more likely to order such tests.^27,28