Data Presented at SABCS 2025 Demonstrated that the Endocrine Activity Index® (EAI®) May Identify Patients Most Likely to Benefit from Extended Endocrine Therapy

HOUSTON, Feb. 16, 2026 /PRNewswire/ -- New data presented at the 2025 San Antonio Breast Cancer Symposium (SABCS) from the NRG/NSABP B-42 trial demonstrated that the Endocrine Activity Index (EAI) identifies postmenopausal women with hormone receptor–positive (HR+), HER2-negative breast cancer who may derive meaningful benefit from extended endocrine therapy. The findings were presented by Eleftherios P. Mamounas, MD, AdventHealth Cancer Institute, Orlando, FL, in a general session on behalf of the NRG Oncology/NSABP investigators, under the title: "Evaluation of the Sensitivity to Endocrine Therapy (SET_ER/PR) assay to predict benefit from extended endocrine therapy in the NRG/NSABP B-42 trial."

Extended endocrine therapy beyond five years can reduce the risk of late breast cancer recurrence, but benefits must be weighed against cumulative side effects. Clinicians have limited options to identify which patients are most likely to benefit from prolonged treatment.

The NRG/NSABP B-42 trial evaluated extended letrozole therapy (ELT) versus placebo in postmenopausal women with HR+ breast cancer who had already completed five years of adjuvant endocrine therapy and demonstrated a small (3.3%) but significant benefit of ELT in this patient population. This new analysis examined whether the EAI test, a genomic signature that measures endocrine activity, could predict benefit from ELT.

Patients with high endocrine activity (EAI ≥ 1.50) experienced a statistically significant and clinically meaningful benefit from ELT, with a 10-year absolute BCFI benefit of 7.1%. Patients with lower EAI values (<1.50) did not experience a statistically significant benefit from extended therapy. This benefit was observed across nodal subgroups and was most pronounced in node-positive patients with high EAI scores, demonstrating a 10.5% absolute reduction in BCFI events compared to placebo. Treated as a continuous variable, higher EAI values were associated with a progressively greater relative benefit from ELT.

"EAI is the only test that can provide insight into how active the estrogen/progesterone pathway of a breast cancer tumor is," said Delphi Diagnostics Chief Medical Officer, Federico A. Monzon. "Data from the B-42 study supports the hypothesis that longer durations of endocrine therapy are most effective for patients whose cancers are highly endocrine-sensitive. This data continues to establish EAI as an important signature that can provide patient-specific insights to support treatment decisions for breast cancer patients."

About EAI
Delphi Diagnostics' Endocrine Activity Index® (EAI™) test can provide actionable information for prognosis and prediction of dose-intense taxane-based chemotherapy benefit in stage II-III, HR+ HER2- breast cancer. The EAI measures endocrine activity in a breast tumor and 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 EAI test has been shown in various studies to be a consistent prognostic indicator for long-term outcomes in stage II-III breast cancer patients, to be independent of other prognostic tests, as well as to be predictive for response to dose-dense chemotherapy.

About Delphi Diagnostics
Delphi Diagnostics Inc. is a Texas-based company focused on advancing clinically valid tests for the prognosis and prediction of breast cancer treatment. Delphi Diagnostics, Inc. holds an exclusive license from The University of Texas MD Anderson Cancer Center in Houston, TX to commercialize the Endocrine Activity Index, a technology that was developed by the laboratory of Dr. W. Fraser Symmans**. The Endocrine Activity Index (EAI) test measures endocrine activity in stage II-III, HR+HER2- breast cancer.  Delphi's vision is to make the EAI test available to breast cancer patients and open new pathways for personalized breast cancer treatment. To learn more, visit www.delphi-diagnostics.com.

**Dr. Symmans has a personal financial relationship with Delphi that has been identified as a conflict of interest with this research and is managed by MD Anderson's Conflict of Interest Committee.

Media Contact:
Emily Granger
Delphi Diagnostics Inc.
[email protected] 
508.341.9331

SOURCE Delphi Diagnostics Inc