Breast cancer screening with mammography in women aged 40-49 years: Impact of length of screening interval on effectiveness of the program.

OBJECTIVES

To estimate the impact on the effectiveness of Swedish breast cancer screening program in women aged 40-49 years of shortening the screening interval from 21 months to 18 or 12 months.

METHODS

The reduction in breast cancer mortality among participants in screening with mammography was previously estimated in the Swedish SCReening of Young women (SCRY) study to be 29%. The expected increased effectiveness with a hypothetical shorter screening interval than the average of 21 months in SCRY was calculated using data about the women who died from breast cancer even though they participated in the SCRY program.

RESULTS

During the study period, 547 women who participated in the index screening round died from breast cancer. Shortening the screening interval to 18 months led to an improved effectiveness of 0.7-3.9% considering interval cancers only and of 1.3-7.6% considering screening-detected cancers only, and for both interval and screening-detected cancers the improvement was 1.9-11.5% when the assumed mortality reduction for the deceased cases varied from 5% to 30%. Shortening the screening interval to 12 months increased the effectiveness by 1.6-9.8% for interval cancers and by 2.9-17.4% for both interval and screening-detected cancers.

CONCLUSION

Shortening the screening interval for women aged 40-49 years to 18 or 12 months might further reduce the breast cancer mortality rate.