Objective: The purpose of our study was to estimate the number of women needed to screen (NNS) to prevent one breast cancer death and the number needed to screen per life-year gained (NNS/LYG) with annual or biennial screening mammography and to compare NNS to the number needed to invite (NNI) to a screening trial to prevent one breast cancer death.
Materials and methods: Cancer Intervention and Surveillance Modeling Network (CISNET) modeling results commissioned by the United States Preventive Services Task Force (USPSTF) for their 2009 update of breast cancer screening recommendations were used to estimate NNS and NNS/LYG with annual or biennial screening mammography. NNS values were compared with NNI as reported by USPSTF, which used the CISNET results to aid their 2009 recommendation of starting age and screening interval.
Results: For women between the ages of 40 and 49 years undergoing annual screening mammography, CISNET modeling results estimate an NNS of 746, 39% of the NNI of 1904 estimated by USPSTF on the basis of randomized controlled trial (RCT) data. The NNS based on CISNET results for women between 50 and 59 years is 351 (26% of the NNI of 1339 estimated by USPSTF from RCT data), for women between 60 and 69 years is 233 (62% of the NNI of 377 estimated by USPSTF from RCT data), and for women between 70 and 79 years is 377. Annual screening of women between 40 and 84 years yields an NNS of 84 and an NNS/LYG of 5.3. Biennial screening of women ages 50-74 yields an NNS of 144 and an NNS/LYG of 9.1.
Conclusion: The NNS based on CISNET modeling results is much smaller than the NNI based on RCT data. Eighty-four women need to be screened annually between 40 and 84 years to save one life from breast cancer and 5.3 need to be screened annually to gain 1 life-year from breast cancer.