Overview
Regular laboratory testing is required to monitor for liver side effects (hepatotoxicity) in patients taking CDK4/6 inhibitors for advanced breast cancer. This study evaluated electronic health record data (EHR) from Flatiron Health Research Databases in the United Kingdom (245 patients), Japan (195 patients), and Germany (205 patients) between 2017 and 2026 to characterize liver function test (LFT) monitoring practices and severe (grade 3+) hepatotoxicity detection rates.
Researchers found that monitoring intensity varied across countries: patients in the UK and Japan received a median of two LFTs per month during the first two months of treatment, compared to one per month in Germany. The upper limit of normal (ULN) tended to be lower in Japan compared with the UK and Germany. Captured severe hepatotoxicity rates were consistent in the UK (6.0%) and Japan (11.0%, after adjustment for ULN differences), whereas Germany recorded a comparatively lower rate (2.5%), reflecting lower testing frequency.
Why this matters
This study demonstrates that structured laboratory data from international EHRs can be harmonized for global drug safety monitoring. It also emphasizes that real-world adverse event detection is strongly linked to local testing practices, providing essential context for interpreting safety data across international healthcare systems and strengthening global drug surveillance.