On December 2, 2024 Agendia, Inc. reported the publication of a pivotal secondary analysis from the IDEAL randomized Phase 3 clinical trial in JAMA Network Open (Press release, Agendia, DEC 2, 2024, View Source [SID1234648742]). The study highlights the ability of the MammaPrint (MP) genomic assay to predict benefit of extended endocrine therapy (EET) in post-menopausal patients with early-stage, hormone receptor positive (HR+) breast cancer.

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The published study, titled Selection of Patients with Early-Stage Breast Cancer for Extended Endocrine Therapy: A Second Analysis of the IDEAL Randomized Clinical Trial, corroborates prior findings published from the NSABP B-42 trial, demonstrating that MP can identify patients who benefit most from EET and those with minimal benefit who can avoid associated side effects, thus optimizing adjuvant treatment decisions beyond traditional clinical risk factors.

This secondary analysis focused on MammaPrint’s predictive capacity of EET in preventing late recurrences among a translational cohort of 515 IDEAL patients. The cohort consisted of post-menopausal, hormone receptor-positive early breast cancer patients who were randomized to receiving 2.5- or 5-years of extended letrozole therapy after completing an initial 5 years of endocrine therapy. The original study did not show any benefit of 5 years over 2.5 years of endocrine therapy, however, through analysis using genomic profiling with MammaPrint, this study was able to identify a subset of patients who will benefit from EET. Key findings from the study include:

Significant benefit for MP Low-Risk Patients: MP Low-Risk patients derived the largest benefit from extended letrozole treatment at 10 years post-randomization. Researchers found an absolute benefit of 10.1% for distant recurrence (DR), 11.7% for recurrence-free interval (RFI), and 9.7% for breast cancer-free interval (BCFI) for MP Low-Risk patients. The effect of letrozole on the 10-year RFI rate was significantly dependent on MammaPrint classification.
No EET Benefit for MP High-Risk Patients: Patients with MP High-Risk tumors are more likely to relapse within the first 5 years of diagnosis and as evidenced by the results of the study, derive less benefit from extending endocrine therapy beyond the initial 5-years post-diagnosis.
Ultra-Low-Risk Findings: Although few patients in the cohort had a MP Ultra-Low tumor, they did not derive any EET benefit for the above endpoints, which is consistent with B42 where a larger number of ultralow patients were analyzed.
"By demonstrating MammaPrint’s ability to predict the benefit from extended endocrine therapy based on genomic risk, particularly the recurrence-free interval for Low-Risk patients, physicians are now better equipped to identify which patients will benefit from this treatment," said Laura van ‘t Veer, PhD, Professor of Laboratory Medicine, Co-Leader of the Breast Oncology Program and Director of Applied Genomics at the Helen Diller Family Comprehensive Cancer Center, University of California, Chief Research Officer and Co-Founder of Agendia. "These findings provide clinicians with a powerful tool to optimize endocrine treatment duration, potentially sparing MP High-Risk patients from unnecessary extended therapy while ensuring MP Low-Risk patients receive the full protective benefits they need."

"These data build upon the evidence gathered from the NSABP-42 study, providing further validation of MammaPrint’s genomic profiling to help refine treatment strategies and identify patients who are more likely to benefit from extended endocrine therapy," said William Audeh, MD, MS, Chief Medical Officer of Agendia. "We know that some hormone-positive breast cancer may have a risk for late recurrences, beyond five years, and these data show that MammaPrint can predict which of those recurrences are preventable by EET. Because MammaPrint looks at the biology of the tumor early in the treatment cycle, it can distinguish Low-Risk patients who will derive substantial benefit from extended endocrine therapy from High-Risk patients who will not. This approach not only optimizes therapeutic efficacy, but also minimizes unnecessary treatment for those unlikely to benefit, thereby enhancing overall patient care."

The data from both IDEAL and NSABP-B42 validate MP’s predictive ability to determine which patients will benefit from EET and which can avoid it, potentially improving long-term survival outcomes and quality of life. These findings expand MP’s clinical utility beyond guiding neoadjuvant and adjuvant chemotherapy decisions and towards optimizing the duration of adjuvant endocrine treatment.