The utility of the 21-gene Oncotype DX Breast Recurrence Score® assay in node-negative breast cancer patients - the final analysis of the Polish real-life survey PONDx.

Introduction: Breast cancer (BC) is among the most frequently diagnosed malignant tumours in females. The optimal treatment of early HR+, HER2-, and lymph node-negative (N0) BC remains challenging. Since individual assessment of recurrence risk and expected benefits from adjuvant chemotherapy (CT) based on clinicopathological features alone appear inadequate, gene expression profiling tests have been developed. This study aimed to evaluate the impact of Oncotype DX Breast Recurrence Score^® (Oncotype DX Breast RS) test results on physicians' decisions concerning adjuvant CT in the Polish population.

Material and methods: The PONDx survey investigated the real-life use of Oncotype DX Breast RS in 204 pa- tients with HR+, HER2-, N0 BC in 8 clinical reference centres in Poland. Data on clinicopathological features and changes in treatment based on the Oncotype DX Breast RS test were collected.

Results: Chemotherapy plus endocrine therapy (ET) was initially recommended in 44.8% and ET alone in 55.2% of patients. After the introduction of recurrence score results, the recommendation for CT decreased significantly: relative reduction of 25.5% (95% CI: 11.7-52.3) and absolute reduction of 11.4% (95% CI: 1.9-21.0). Among patients initially recommended for CT, treatment was de-escalated in 62.2%; conversely, among patients initially recommended for ET alone, 29.7% were escalated to CT after testing. The relative reduction was especially pronounced in post-menopausal patients (29.6%) and in those with lobular BC (42.9%).

Conclusions: The Oncotype DX Breast RS result significantly influenced treatment decisions, with 44.3% of patients changing treatment, thus avoiding overtreatment or undertreatment. The Oncotype DX Breast RS test improves patient management and increases physician confidence in treatment recommendations.