DO NOT SCREEN FOR CANCER PEOPLE WITH SHORT LIFE EXPECTANCY 

Screening for breast and colorectal cancer should be targeted at individuals who have a life expectancy greater than 10 years. Otherwise, the harms may outweigh the benefits of screening, according to a study published online January 8 inBMJ.

This conclusion comes from a meta-analysis of survival data from Denmark, Sweden, the United Kingdom, and the United States conducted by Sei J. Lee, MD, assistant professor of medicine at the University of California, San Francisco, and colleagues.

The researchers found that in populations primarily older than 50 years, it took an average of 4.8 years to prevent 1 death from colorectal cancer in 5000 people undergoing of fecal occult blood test screening.

This suggests that the harms of screening outweigh the benefits for most people with a life expectancy of less than 5 years. In addition, it would take 10.3 years to prevent 1 death from colorectal cancer for every 1000 patients screened, which indicates that for most people with a life expectancy greater than 10 years, the benefits likely outweigh the harms.

Results were similar for breast cancer. It took 3.0 years before 1 death from breast cancer was prevented in 5000 women screened with mammography, and 10.7 years before 1 death was prevented in 1000 women screened.

"Therefore, patients with a life expectancy greater than 10 years should be encouraged to undergo screening for colorectal cancer and breast cancer," the researchers write. "Conversely, patients whose life expectancy is less than 3 to 5 years (that is, less than the time lag to an absolute risk reduction of 1 in 5000) probably should be discouraged from screening, since the potential risks probably outweigh the small probability of benefit," they explain.

However, they caution that these results should not be used to deny screening for people with a limited life expectancy. "Rather, our results should inform individualized decision making, which aims to account for patient preferences and values while maximizing benefits and minimizing risks," Dr. Lee and colleagues note.

Defining the Time Lag

The researchers analyzed the results of 5 breast and 4 colorectal cancer screening trials with populations predominantly older than 50 years. All were population-based randomized controlled trials that compared screened with unscreened populations. All of the studies were identified as high quality by the Cochrane Collaboration and the US Preventive Services Task Force.

The primary end point was the time to death from breast or colorectal cancer in screened and unscreened populations. The studies used fecal occult blood testing for colorectal cancer screening and mammography for breast cancer screening.

The researchers note that screening for these 2 cancers can find asymptomatic cancer at an early stage, which, if not treated, can cause symptoms or even death years later. Therefore, screening has a "time lag to benefit" — from the screening date, when the person is exposed to the potential risks of screening, to the point when benefits can be observed in clinical trials.

However, it remains unclear just how long a person needs to live to potentially derive a survival benefit from screening. Randomized controlled trials of screening tend to focus on the magnitude of benefit, rather than when those benefits actually occur, the researchers explain, which has led to differences in recommendations about the time lag to benefit.

To determine the screening time lag to benefit, the researchers calculated the number of years needed to reach different thresholds of benefit, using the absolute risk reduction in cancer-specific mortality. These absolute risk reductions ranged from preventing 1 cancer death per 10,000 people screened to preventing 1 cancer death per 500 people screened.

They found that mortality benefits varied in the studies, but that the benefit in colorectal cancer mortality rose steadily with longer follow-up periods; at 15 years, 23 colorectal cancer deaths were prevented for 10,000 people screened.

This was also true for breast cancer screening; at 15 years, the benefit of mammography increased to 19 deaths prevented for 10,000 women screened.

They note serious harms in 3 in 10,000 people screened for colorectal cancer and in 1 in 1000 screened for breast cancer. Therefore, an absolute risk reduction of 1 in 1000 is probably a reasonable threshold at which the potential benefit will likely outweigh the potential risk in most people.

The study was supported by the Veterans Affairs Medical Center, San Francisco, California. The authors have disclosed no relevant financial relationships.

BMJ. 2013;345:e8441. Full text