Genomic Test Guides Taxane-Based Chemotherapy Selection in Breast Cancer

Selecting adjuvant chemotherapy for hormone receptor–positive, HER2-negative (HR+/HER2−) breast cancer remains challenging because current genomic assays mainly estimate recurrence risk rather than predict response to specific treatments. Researchers have investigated whether tumor endocrine signaling can identify sensitivity to taxane-based therapies. A new peer-reviewed study reports that a genomic assay can distinguish which HR+/HER2− tumors are most likely to benefit from adjuvant weekly paclitaxel.

Delphi Diagnostics’ (Houston, TX, USA) Endocrine Activity Index (EAI) is designed to quantify endocrine activity within a breast tumor. For prognostic use, the Index Score is adjusted for baseline prognosis using molecular subtype genes (RNA4) and clinical factors such as tumor size and regional lymph node involvement. The company reports that EAI can provide actionable information for prognosis and prediction of benefit from dose‑intense taxane-based chemotherapy in stage II–III HR+ /HER2− breast cancer.

Findings were published in Clinical Cancer Research on May 26, 2026 in a prospective‑retrospective analysis of the GEICAM/9906 randomized phase III trial. Investigators assessed tumor samples and outcomes from patients who received anthracycline-based chemotherapy with or without weekly paclitaxel. Patients whose tumors showed very low endocrine activity—an EAI score below 0.75—experienced significantly improved distant recurrence‑free outcomes when weekly paclitaxel was added, whereas patients with higher endocrine activity did not demonstrate additional benefit from paclitaxel.

According to the report, approximately 16% of HR+ /HER2− tumors exhibited low endocrine activity and were associated with improved outcomes on weekly paclitaxel–containing therapy. The analysis independently validates earlier findings and is presented as establishing EAI as the first genomic assay shown to predict benefit from a contemporary taxane-based chemotherapy regimen in HR+ /HER2− disease. The results also build upon prior clinical evidence by demonstrating reproducibility across two independent randomized clinical trials and support the use of biologically informed treatment selection to avoid exposure to regimens unlikely to provide benefit.

"This study represents an important milestone for precision oncology and provides independent confirmation that endocrine activity within an HR+ /HER2− breast tumor can predict sensitivity to specific chemotherapy approaches," said Federico A. Monzon, MD, Chief Medical Officer at Delphi Diagnostics. "These findings support the potential for EAI to help clinicians personalize treatment decisions and select chemotherapy regimens more likely to benefit individual patients."

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