Patients with life expectancy of less than 10 years derive little benefit from screening

“Time lag to benefit after screening for breast and colorectal cancer: meta-analysis of survival data from the United States, Sweden, United Kingdom, and Denmark. By S.J. Lee and colleagues, British Medical Journal.

Clinical practice guidelines recommend targeting breast and colorectal cancer screening to healthy older patients who have a substantial life expectancy. Cancer screening is unlikely to benefit patients with a short life expectancy because the benefit from screening is not immediate. Screening leads to benefit by finding an asymptomatic cancer at an early stage which, if left untreated, would cause symptoms or death years later.

Thus, screening interventions have a “time lag to benefit.” This period starts from the date of screening, when the patient is exposed to the risks of screening (e.g., pain, worry, and potential complications such as perforation or infection) to the point when the benefits (e.g., reduction in cancer mortality) are observed in randomized screening trials.

To examine time lag to benefit, Lee and colleagues performed a meta-analysis of five mammography trials and four trials of fecal occult blood testing (FOBT). The mammography trials involved 13,811 to 61,004 patients, and follow-up ranged from 10 to 20 years. Investigators limited their analysis to women ages 55 to 74. The primary outcome of all the trials was breast cancer mortality.

The mammography analyses showed that one breast cancer death would be prevented every 10.7 years for every 1,000 women screened. The frequency of serious harm was estimated at three in 10,000 for breast cancer screening. The authors conclude that “screening for breast and colorectal cancer is most appropriate for patients with a life expectancy greater than 10 years. Incorporating time lag estimates into screening guidelines would encourage a more explicit consideration of the risks and benefits of screening for breast and colorectal cancer.”

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