All of the randomized controlled trials of mammography, with or without clinical breast exam have published updates since 1996 and now have between 10.5 and 20 years of follow-up. In our meta-analysis combining all studies of fair quality, the summary relative risk reduction for breast cancer screening among women of all ages was 0.84 (95% credible interval [CrI], 0.77-0.91), and the overall number needed to screen to prevent one death from breast cancer over approximately 14 years of observation was 1,224 (95% CrI, 665-2,564). These numbers reflect not just one screening, but multiple screenings in an organized program.
Six fair or better quality randomized trials provided information about the efficacy of mammography and clinical breast exam among women younger than age 50. In our meta-analysis, the summary relative risk for the six studies was 0.85 (95% CrI, 0.73-0.99), and the overall number needed to screen was 1,792 (95% CrI, 764-10,540). Analyses of the trials to determine the portion of the benefit attributable to screening before age 50 have mixed results, but suggest that a significant portion of the benefit is due to screening before age 50, especially in women who were aged 39 to 44 when they had their first mammogram.
No study has compared clinical breast examination to no screening. In trials that combined mammography with clinical breast examination, the contribution of clinical breast examination to reduced mortality from breast cancer is unclear. One study compared annual clinical breast examination plus mammography to a baseline clinical breast examination in women aged 40 to 49 at study entry and found no difference in breast cancer mortality. The role of breast self-examination in reducing breast cancer mortality has been evaluated in 2 randomized controlled trials and 1 non-randomized controlled trial, and none have shown benefit.
