Improving breast cancer screening workflows with machine learning
Google Research’s AIMS studies evaluated whether machine learning could support the UK’s mammography double-reading workflow. Across five NHS screening services, the AI system improved cancer detection sensitivity without reducing specificity, detected some cancers missed by human readers, and processed cases far faster. The studies also showed that safe deployment requires local calibration, monitoring for distribution shifts, and evaluation of how clinicians interact with AI results. ## NHS Screening Challenges - The UK NHS uses two human readers for each mammogram, with arbitration when their assessments require review. - A projected shortage of clinical radiologists—currently around 30% and expected to reach 40% by 2028—threatens the sustainability of this model. - AI could help increase detection while reducing pressure on radiology services. ## Study 1: Standalone Performance - The retrospective evaluation included mammograms from approximately 116,000 women screened across five NHS services. - The services represented three different double-reading and arbitration workflows. - AI thresholds were calibrated separately for each service to account for local populations and procedures. - Performance was measured against the original first reader using a 39-month follow-up period, including interval and subsequent-round cancers. - Researchers also assessed: - Comparisons with second and consensus readers - Lesion-level localization - Performance across demographic groups ## Study 1: Results - Cancer detection increased from 7.54 to 9.33 cases per 1,000 women. - The AI system achieved significantly higher sensitivity than the original first reader without compromising specificity. - It detected 25% of interval cancers missed by the original double-reading process. - Performance was especially strong for invasive cancers and women attending their first screening. - The study found no notable systematic disparities by age, ethnicity, breast density, or socioeconomic status. ## Prospective Technical Deployment - The system was deployed non-interventionally at 12 sites across two London screening services. - It processed 9,266 cases over roughly two months per service. - Mammograms were pseudonymized and sent to a secure Google Cloud-based system. - Median AI processing time was 17.7 minutes, compared with more than two days for the first human read. - The deployment detected a distribution shift between historical training data and current clinical data. - Researchers adjusted operating points during deployment to maintain safe and appropriate recall rates for local workflows. ## Study 2: AI in the Double-Reading Workflow - The second study examined how human readers performed when using AI as part of arbitration, rather than evaluating AI in isolation. - Twenty-two readers reviewed thousands of cases using real screening-service rules. - Two workflows were compared: - **Standard care:** decisions from the historical first and second human readers - **AI-enabled care:** the historical first-reader decision paired with the AI decision - This design aimed to assess the practical effects of replacing the second human read with an AI reader. The findings support AI as a potential second reader in breast cancer screening, but broader prospective clinical validation is still needed. Successful adoption should include phased deployment, local calibration, continuous monitoring, and careful evaluation of human-AI decision-making.
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