INTRODUCTION: Gene expression assays, such as the MammaPrint® (Agendia, Amsterdam, the Netherlands) 70-gene signature, are increasingly used by oncologists to understand breast cancer biology and improve treatment planning. This study assesses the utility of MammaPrint genomic risk in predicting treatment outcomes for women with breast cancer in a retrospective German cohort with a 10-year follow-up, treated based on clinicopathological features alone.

METHODS: The sample set of 117 tumours from the ‘Patients Tumour Bank of Hope’ (PATH) biobank with 10-year follow-up were classified using MammaPrint into high or low risk of distant metastasis. Patients were previously treated according to St. Gallen and Adjuvant! Online high- or low-risk criteria. Statistical analyses compared overall survival (OS) and treatment outcomes between clinical and genomic risk groups.

RESULTS: Among the 78 patients with clinically high-risk tumours, 50% (39) were reclassified as MammaPrint low risk. In total, 57.3% (67/117) patients with MammaPrint low-risk tumours demonstrated a significantly higher 10-year OS of 93.4%, irrespective of nodal status, compared to patients with MammaPrint high-risk tumours (71.2%; p=0.001). Chemotherapy improved OS in patients with MammaPrint high-risk tumours by 29.4%, but not for patients with MammaPrint low-risk tumours (p=0.016). Discussion: The findings confirm the prognostic utility of MammaPrint for identifying genomically low-risk patients who may safely omit chemotherapy while suggesting genomically high-risk cases may benefit from chemotherapy. By providing a more precise assessment of cancer risk than traditional clinicopathological methods alone, MammaPrint may help reduce unnecessary treatments and improve long-term quality of life for patients diagnosed with early-stage breast cancer.

KEY POINTS:

1. The prognosis in early breast cancer is based on the underlying personal risk of recurrence.
2. To receive more detailed information on the breast cancer biology of a given patient, more information is needed for individualised treatment recommendations to avoid unnecessary over- and undertreatment.
3. Multi-gene assays such as the MammaPrint 70-gene signature provide this information to allow classical prognostic information such as ‘clinical risk’ into ‘genomic risk’ to be transformed to gain more information on tumour biology and optimise the early breast cancer therapy.