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Comment & Response
September 16, 2021

Is Colorectal Cancer Screening Absolutely Beneficial for Older Adults?

Author Affiliations
  • 1Division of Biostatistics and Bioinformatics, Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University, Baltimore, Maryland
  • 2Division of Geriatric Medicine and Gerontology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland
JAMA Oncol. 2021;7(11):1728. doi:10.1001/jamaoncol.2021.4152

To the Editor In their cohort study, Ma et al1 have shown that screening for colorectal cancer (CRC) was associated with lower relative risks of CRC and of CRC-related mortality. For public health interventions aimed at preventing rare outcomes, absolute risk reduction, rather than relative risk reduction, is most important. The number needed to treat (NNT), which is the reciprocal of absolute risk reduction, is a simple metric for assessing the pragmatic outcome of interventions.2 The NNT is the number of people who need to be treated to prevent 1 additional outcome. An intervention with a large NNT is of questionable utility, especially if it also carries substantial harms. In the context of screening, we can use the term number needed to screen (NNS). The authors report CRC incidence rates of 489 of 246 717 and 172 of 138 592, in unscreened and screened older adults (>75 years), respectively.1 This translates to an NNS of 1350, ie, screening prevents 1 incident case of CRC in older adults for every 1350 person-years. The authors also report CRC-related mortality rates of 212 of 289 036 and 111 of 169 640, in unscreened and screened older adults, respectively, which translates to an NNS of 12 635. This means that screening prevents 1 CRC-related death in older adults for every 12 635 person-years.

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