A 5-year review of genomic medicine in breast cancer: insights from C-CAT data on 3776 Japanese patients.

Abstract

Background: In Japan, despite 5 years since CGP tests were covered by insurance in 2019, low drug accessibility rates remain a critical issue. We evaluated drug accessibility in 3776 breast cancer from the C-CAT database using two criteria: the proportion first linked to PMDA-approved drugs with phase III trial evidence for breast cancer through CGP tests but not existing Companion diagnostics [CDx] (*), and the proportion first linked to PMDA-approved drugs including based on phase I and II trial evidence (**). Additionally, cases linked to investigational drugs for non-PMDA-approved drugs were counted.

Methods: We identified the top 100 genetic alterations in Japanese breast cancer via CGP tests, listing corresponding drugs from C-CAT reports. Drug accessibility was re-evaluated through simulations with updated evidence levels by a member of the expert panel at Osaka University (EP-EL in OUH).

Results: Results showed the proportion improved to 28.4% under the newest EP-EL in OUH, including 3.4% for HER2-negative cases eligible for HER2-targeted therapy due to ERBB2 amplification and 25.0% for ER-positive, HER2-negative cases eligible for capivasertib-fulvestrant therapy due to PIK3CA, AKT1, and PTEN alterations (*). However, in part, initial false negatives for HER2 status and practical difficulties in using CGP tests as a CDx for capivasertib exist. Including mutations like TMB-H, MSI-H, BRAF V600E mutation, and NTRK fusions raised the proportion to 37.9% (**), but lacking drugs with phase III trials evidence.

Conclusion: These findings highlight the ongoing difficulties in demonstrating clear clinical utility of CGP tests in Japan, emphasizing the need for broad discussions on its future direction.