Screening for breast and colorectal cancer is most appropriate for patients with a life expectancy of more than 10 years, according to a study published last week in BMJ.
Researchers analyzed the results of five breast and four colorectal screening trials that took place in the U.S., U.K., Sweden and Denmark. For breast cancer the researchers focused on major trials of mammography, while for colorectal cancer screening, the researchers focused on fecal occult blood tests rather than flexible sigmoidoscopy or colonoscopy.
The researchers' objective was to determine the amount of time between screening and when the benefits of screening are seen in order to determine whether an individual patient is likely to benefit from screening.
The trials were published between 1986 and 2008 and involved anywhere from 40,000 to 150,000 subjects, with follow-up ranging from eight to 20 years. The age of the patients enrolled in the trials ranged from 45 to 80 years.
The researchers determined that it took an average of 4.8 years to prevent one death from colorectal cancer for 5,000 people screened, and 10.3 years to prevent one death for 1,000 people screened. For breast cancer it took an average of three years to prevent one death for 5,000 women screened, and 10.7 years to prevent one death for 1,000 people screened.
The frequency of serious harm from screening, according to the authors, has been estimated at three in 10,000 for breast cancer screening, and one in 1,000 for colorectal cancer screening. Consequently, "an absolute risk reduction of one in 1000 is probably a reasonable threshold where the potential benefit likely outweighs the potential risks for most patients," the study's authors wrote.
"Therefore," they continued, "patients with a life expectancy greater than 10 years should be encouraged to undergo screening for colorectal cancer and breast cancer. Conversely, patients whose life expectancy is less than three to five years (that is, less than the time lag to an absolute risk reduction of one in 5000) probably should be discouraged from screening, since the potential risks probably outweigh the small probability of benefit."
- see the article in BMJ