Implementing MyChoice® CDx HRD testing for the Nordics: lessons from 2021 to 2023.

Background: Assessment of homologous recombinant deficient (HRD) phenotypes is key for managing Poly (ADP-ribose) polymerase inhibitor (PARPi) treatment. To accommodate the need for a validated HRD platform and enhance targeted treatment of ovarian cancer patients, a Nordic core facility for the myChoice® CDx platform was established in Denmark.

Materials and methods: Comparative calculations and statistics are based on information from test requisitions and results (Genome Instability Score [GIS], BRCA status and combined HRD status) obtained from ovarian and breast cancer samples submitted for HRD-testing by myChoice® CDx through the Nordic core facility in the 2-year period.

Results: Copenhagen University Hospital received 1,948 requisitions during the 2-year period. Conclusive results were obtained in 89% of the tests, while 7% were inconclusive due to the lack of GIS and 4% were not able to be analysed. Comparing the conclusive HRD status results across countries, Sweden had the highest percentage of HRD positives (38%) compared to Denmark, Norway, and Finland (28-32%).

Interpretation: The myChoice® CDx Nordic core facility has been well received among the Nordic countries and provides new insights on the influence of national guidelines on HRD testing. Overall, we experienced an efficient turnaround time and a high fraction of conclusive results. Interestingly, prior somatic BRCA testing is redundant when assessing HRD status through myChoice® CDx test since somatic BRCA screening is already a significant component of the myChoice® CDx test. Thus, it should be considered to omit prior somatic BRCA testing to ensure a rationalised HRD diagnostic flow optimised for clinical use.