Colorectal cancer screening in kidney disease patients: working backwards.

Periodic colorectal cancer (CRC) screening in the general population receives one of the highest recommendations from the US Preventative Health Care Services Task Force and many other practice guideline organizations based on consistent strong evidence from clinical trials. However, the evidence is for subjects at average risk with average life expectancies. In this journal, Wong et al. examine the net benefit and cost-effectiveness of CRC screening in dialysis patients not on the wait list, dialysis patients wait-listed for a kidney transplant and kidney transplant recipients. The benefits of screening were estimated to be 2.6 added days of life for each dialysis patient, 6.9 days for wait-listed patients and 12 days for those transplanted. The benefits accruing to kidney transplant patients were much less than their earlier study showing a benefit of 24 days, probably because the model assumed the transplanted graft never failed. Not surprisingly the cost-effective ratios are high in the former two groups but reasonable in the transplanted population. Although there is a lack of direct evidence, these and other modeling studies suggest the benefits of CRC screening in patients with functioning kidney transplants may well be equivalent to the benefit in the general population. Given the potential harm of screening and the short life expectancies of dialysis patients, the benefits of CRC screening will be small and uncertain. Not screening many of our older dialysis patients would be consistent with guideline recommendations that CRC screening only be undertaken in patients with life expectancies of >10 years. Cancer prevention is high on the healthcare wish lists of both provider and patient [1]. However, there is nothing more controversial than screening to prevent cancer. Whether there has been a recent catharsis or simply a swing in the pendulum, many are not happy with the trend that sees guidelines pulling back with reductions in the frequency of screening, recommendations that screening be delayed to older ages or ceased at a certain age and recognition that some patients are currently inappropriately screened [2]. It is ironic that some cancers such as prostate cancer are frequently screened for in men yet the evidence of benefit is weak, whereas participation rates are relatively low for colorectal cancer (CRC) screening where the evidence of benefit is strongest [3]. A great deal of thought and effort is expended in finding the right balance. Nonetheless, cancer interest groups will always argue that any evidence of benefit is reason enough, whereas task forces believe that there must be strong unbiased evidence (randomized trials of screening) that show significant benefits in hard endpoints (lives saved) and that these benefits must significantly outweigh any potential harms of screening. Like all population screening strategies, the benefits are for the few while requiring participation of many. It is also the many that are potentially subjected to the harms. There are the risks of false-positive screens that result in unnecessary psychological distress, intrusion of time and invasive procedures, finding indolent lesions that may never pose a risk to an individual patient (length bias), later risks associated with further invasive testing and treatment or simply finding lesions earlier with no impact on overall outcomes (lead bias). The erosion of length and quality of life from these harms is not always appreciated nor captured. These have only recently been enumerated in detail for breast and prostate cancer screening and the analyses have been sobering. A recent study on prostate cancer shows the net benefits may be eroded completely by diagnosis and treatment complications and their effects on quality of life [4]. Most importantly, the recommendations to screen are for average risk patients with average life expectancies or for screening in higher risk populations. However, there has been an undercurrent that all patients should have the right to screening, not to do so is an error of omission, and quality of care can be measured by examining screening rates [5]. In fact, the USRDS at one time tracked prostate and breast cancer screening in US dialysis patients as a measure of quality care [6]. The issues become complex in subpopulations with reduced life expectancies and even more so if these populations are at increased cancer risk. The chronic kidney disease (CKD) population is very much an example where the recommendations might blur. Most agencies do not recommend CRC screening in patients with life expectancies <5 years, since the benefits of detecting early lesions that become problematic IN F O C U S