Most individuals with a life expectancy less than three to five years should bypass screening mammography and fecal occult blood testing, researchers reported in a study published Jan. 8 in British Medical Journal. However, the authors stressed the results should not be used to deny screening for individuals with limited life expectancy.
Cancer screening guidelines recommend targeting screening to older patients with a substantial life expectancy due to a time lag between the screening exam and the realization of benefits from screening. However, research has not yet determined a life expectancy threshold needed to benefit from breast and colorectal cancer screening.
Sei J. Lee, MD, from University of California, San Francisco, and colleagues conducted a survival meta-analysis of five major mammography trials and four fecal occult blood testing trials to calculate the exams’ time lag to benefit.
After pooling the results of the screening mammography trials, Lee and colleagues determined three years were required before one breast cancer death was prevented for 5,000 women screened and 10.7 years were required before one death was prevented for 1,000 women screened.
The results of the colorectal cancer screening trials indicated 4.8 years were required to prevent one colorectal cancer death for 5,000 individuals screened and 10.3 years elapsed before one death was prevented per 1,000 people screened.
The findings suggest individuals with a life expectancy greater than 10 years should be counseled to participate in screening exams for breast and colorectal cancer, and those with life expectancies less than three to five years should be discouraged form screening.
Lee et al described individuals falling between these categories as in “an intermediate zone of small or unclear benefit.” For such patients, individual preferences and values should play a large role in the decision to screen or not. The current findings, they continued, should inform individualized decision making.
The researchers acknowledged several limitations to the study. The trials focused on multiple screening rounds, while the mortality benefit from one round of screening is less than multiple rounds. Thus, the results may have underestimated the time lag for one screening exam.
In addition, screening provides other benefits, such as avoidance of symptoms, which have a shorter time lag than the mortality lag.
Finally, the trials included were older. More current screening methods may result in a different time lag to benefit. Lee and colleagues plan to apply their methods to ongoing studies of screening colonoscopy. They also noted the need for patient level data in future research. Inclusion of such data could minimize uncertainty and provide more precise estimates of the time lag to benefit, according to Lee et al.
“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,” the researchers concluded.