ABSTRACT
Early detection of breast cancer through screening can lower breast cancer mortality rates and reduce the burden of this disease in the population. In most western countries, mammography screening starting from age 50 is recommended. However, there is debate about whether breast cancer screening should be extended to younger women. This systematic review provides an overview of the evidence from RCTs on the benefits and harms of breast cancer screening with mammography in women aged 40-49 years. The quality of the evidence for each outcome was appraised using the GRADE approach. Four articles reporting on two different trials-the Age trial and the Canadian National Breast Screening Study-I (CNBSS-I)-were included. The results showed no significant effect on breast cancer mortality (Age trial: RR 0.93 (95% CI 0.80-1.09); CNBSS-I: HR 1.10 (95% CI 0.86-1.40)) nor on all-cause mortality (RR 0.98, 95% CI 0.93-1.03) in women aged 40-49 years offered screening. Among regularly attending women, the cumulative risk of experiencing a false-positive recall was 20.5%. Over-diagnosis of invasive breast cancer at 5 years post-cessation of screening for women aged 40-49 years was estimated to be 32% and at 20 years post-cessation of screening to be 48%. Including ductal carcinoma in situ, these numbers were 41% and 55%. Based on the current evidence from randomised trials, extending mammography screening to younger age groups cannot be recommended. However, there were limitations including relatively low sensitivity of screening and screening attendance, insufficient power, and contamination, which may explain the nonsignificant results.