HOUSTON, Texas, Feb. 16, 2026 — New data presented at the 2025 San Antonio Breast Cancer Symposium (SABCS) reveal that the Endocrine Activity Index® (EAI®) genomic test can identify postmenopausal women with hormone receptor–positive (HR+), HER2-negative breast cancer who are most likely to benefit from extended endocrine therapy. Findings from the landmark NRG/NSABP B-42 clinical trial highlight the growing role of precision diagnostics in guiding long-term treatment decisions and optimizing therapeutic benefit beyond the standard five-year endocrine therapy window.
Science Significance
The study provides compelling scientific validation for tumor endocrine pathway activity as a predictive biomarker for extended endocrine therapy response. Endocrine therapy remains a cornerstone of HR+ breast cancer treatment, yet recurrence risk persists long after initial therapy completion. The EAI assay measures estrogen and progesterone signaling activity within tumor biology, offering a genomic readout of endocrine sensitivity.In the B-42 analysis, patients with high endocrine activity (EAI ≥ 1.50) demonstrated a statistically significant improvement in outcomes when treated with extended letrozole therapy. A 7.1% absolute benefit in 10-year breast cancer–free interval (BCFI) was observed, with even greater benefit — 10.5% risk reduction — in node-positive populations. Conversely, patients with low endocrine activity derived minimal benefit, underscoring the assay’s predictive specificity. These findings reinforce the scientific shift toward biomarker-driven duration strategies in hormone therapy.
Regulatory Significance
In the B-42 analysis, patients with high endocrine activity (EAI ≥ 1.50) demonstrated a statistically significant improvement in outcomes when treated with extended letrozole therapy. A 7.1% absolute benefit in 10-year breast cancer–free interval (BCFI) was observed, with even greater benefit — 10.5% risk reduction — in node-positive populations. Conversely, patients with low endocrine activity derived minimal benefit, underscoring the assay’s predictive specificity. These findings reinforce the scientific shift toward biomarker-driven duration strategies in hormone therapy.The B-42 dataset strengthens the evidence base required for diagnostic regulatory submissions, label integration, and guideline inclusion. As regulators increasingly emphasize precision medicine, validated genomic tools like EAI may influence drug labeling, post-marketing evidence requirements, and real-world data collection strategies.
Business Significance
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The B-42 dataset strengthens the evidence base required for diagnostic regulatory submissions, label integration, and guideline inclusion. As regulators increasingly emphasize precision medicine, validated genomic tools like EAI may influence drug labeling, post-marketing evidence requirements, and real-world data collection strategies.The company’s exclusive licensing agreement with The University of Texas MD Anderson Cancer Center strengthens intellectual property protection and commercialization pathways. Positive trial validation may drive laboratory adoption, payer coverage expansion, and biopharma partnerships, especially with endocrine therapy manufacturers seeking companion diagnostics to differentiate treatment strategies.
Patients’ Significance
The company’s exclusive licensing agreement with The University of Texas MD Anderson Cancer Center strengthens intellectual property protection and commercialization pathways. Positive trial validation may drive laboratory adoption, payer coverage expansion, and biopharma partnerships, especially with endocrine therapy manufacturers seeking companion diagnostics to differentiate treatment strategies.The EAI test introduces a personalized risk-benefit framework, enabling physicians to tailor therapy duration based on tumor biology rather than population averages. High-EAI patients may gain life-extending benefit, while low-EAI patients could potentially avoid unnecessary long-term toxicity — marking a significant advance in survivorship care planning.
Policy Significance
The EAI test introduces a personalized risk-benefit framework, enabling physicians to tailor therapy duration based on tumor biology rather than population averages. High-EAI patients may gain life-extending benefit, while low-EAI patients could potentially avoid unnecessary long-term toxicity — marking a significant advance in survivorship care planning.The integration of predictive endocrine biomarkers into treatment pathways may influence clinical guidelines, payer coverage decisions, and national cancer control strategies. As extended therapy becomes more selective, policy frameworks will need to support equitable access to validated genomic testing.
The SABCS 2025 findings position the Endocrine Activity Index® as a transformative genomic tool capable of refining endocrine therapy duration decisions in HR+ breast cancer. By demonstrating that tumor endocrine signaling activity predicts long-term therapeutic benefit, the study advances precision oncology beyond drug selection and into treatment timing optimization. As diagnostic validation progresses, EAI may play a central role in shaping personalized survivorship strategies and improving long-term breast cancer outcomes.
Source: Delphi Diagnostics Inc. press release
