Does screening reduce mortality or hospital admission?

Efficacy of Screening in Reducing Mortality or Hospital Admission

Screening significantly reduces mortality, with mammography screening demonstrating a 40% reduction in breast cancer mortality in women who are actually screened, making it the only screening modality proven to decrease breast cancer mortality. 1

Evidence for Mortality Reduction from Cancer Screening

Breast Cancer Screening

• Mammography is the only screening modality conclusively shown to decrease breast cancer mortality, with multiple randomized controlled trials demonstrating at least a 22% reduction in breast cancer mortality 1
• The Swedish Two-County trial showed a 27-31% reduction in breast cancer mortality after 29 years of follow-up in women aged 40-74 years invited to screening 1
• Observational studies from population-based service screening programs demonstrate even larger mortality reductions (40%) in women who actually received screening compared to those who were only invited 1
• Annual screening mammography for women 40-84 years decreases mortality by 40% (12 lives per 1,000 women screened), whereas biennial screening for women 50-74 years only decreases mortality by 23% (7 lives per 1,000 women screened) 1

Age-Specific Benefits

• For women aged 40-49 years, screening demonstrates a mortality reduction of 48% (RR 0.52; 95% CI, 0.4-0.67) among those exposed to screening 1
• Women aged 50-69 years show a 44% (RR 0.56; 95% CI, 0.49-0.64) reduction in mortality when exposed to screening 1
• The number needed to screen (NNS) to prevent one breast cancer death varies by age group:
  • For women aged 40-49 years: 726 women need to be screened 5-6 times over 10 years 1
  • For women aged 50-51 years: 111-143 women need to be screened biennially until age 69 1

Impact on Advanced Disease Detection

• Screening reduces the risk of being diagnosed with advanced breast cancer:
  • 45% reduction in tumors >2cm for women aged 40-49 years (RR 0.55; 95% CI, 0.46-0.66) 1
  • 33% reduction in tumors >2cm for women aged 50-69 years 1
• Screen-detected tumors are typically lower stage (smaller and more likely to be node-negative) compared to cancers detected by palpation, which decreases treatment morbidity 1
• Advanced breast cancer is reduced for women aged 50 years or older (RR 0.62; 95% CI, 0.46-0.83) but not significantly for those aged 39-49 years (RR 0.98; 95% CI, 0.74-1.37) 2

Effectiveness of Different Screening Approaches

• Mortality reduction is greater when screening begins at age 40 rather than 45 or 50 years, and when performed annually rather than biennially 1
• Digital breast tomosynthesis (DBT) has shown improved cancer detection rates and decreased recall rates compared to digital mammography 1
• Provider assessment and feedback interventions can effectively increase screening rates for mammography, Pap tests, and fecal occult blood tests 3
• Client reminders, small media, and one-on-one education have effectively increased screening for breast and cervical cancer 4
• Reducing structural barriers and out-of-pocket costs has effectively increased breast cancer screening 5

Potential Harms and Limitations

• Approximately 10% of screening mammograms result in recall for additional imaging, although less than 2% lead to biopsy recommendations 1
• Overdiagnosis estimates vary widely, with adjusted estimates ranging from 1-10%, increasing with age at screening 1
• More frequent screening increases false-positive probability (69% for annual vs. 21% for biennial screening over a decade for women 40-49 with dense breasts) 6
• Higher biopsy rates are associated with more frequent screening (12% for annual vs. 3% for biennial screening) 6
• Radiation exposure is a concern, particularly for younger women 6

Special Considerations for High-Risk Women

• Women with genetic mutations or ≥20% lifetime risk should receive annual MRI starting at age 25-30 and annual mammography between ages 25-40 6
• Women with personal history of breast cancer diagnosed before age 50 or with dense breast tissue should undergo annual mammography and MRI 6
• Women with history of chest radiation should undergo annual MRI beginning at age 25 or 8 years after radiation therapy, whichever is later 6

Clinical Implications

• Despite varying guidelines due to different perceptions of risks and benefits, the evidence consistently supports that screening mammography saves lives 1
• Women generally value early detection of breast cancer over concerns about false-positives and screening-related anxiety 1
• The balance of benefits to harms is favorable, with approximately twice as many lives saved compared to cases overdiagnosed 1