New data were presented at the 2021 San Antonio Breast Cancer Symposium demonstrating that the Breast Cancer Index (BCI) may predict preferential recurrence-prevention benefit from extended endocrine therapy and may also predict the overall benefit/risk and likelihood of improved health outcomes from extended endocrine therapy in certain patients with hormone receptor–positive breast cancer. A second study also confirmed that the two biomarkers used in BCI are interconnected molecular drivers of assessing recurrences in hormone receptor–positive breast cancer. These findings were presented in Spotlight Sessions at the Symposium.
Breast Cancer Index is a gene expression–based test that provides information to help physicians individualize treatment decisions for patients with early-stage, hormone receptor–positive breast cancer. The test helps oncologists and patients navigate the difficult trade-offs between taking steps to prevent recurrence of their disease and facing significant side effects and safety challenges related to unnecessary treatment.
“Extended endocrine therapy often comes with tolerability challenges and even significant adverse events,” said study author Marc Buyse, ScD, Associate Professor of Biostatistics at Hasselt University in Belgium. “We found the data to have considerable implications for patient compliance and joint decision-making with their health-care providers, as patients have a more comprehensive picture of the net benefit of staying on extended endocrine therapy so they can better assess the challenges that can come with treatment.”
Prediction of Net Treatment Benefit of Extended Endocrine Therapy
Research has shown that extended endocrine therapy may reduce the long-term risk of recurrence in hormone receptor–positive breast cancer, but treatment is often accompanied by serious adverse events, such as bone toxicity, endometrial cancer, embolisms, heart disease and more. The Net Treatment Benefit (NTB) study (Abstract PD15-04), which examined novel patient subset data (n = 908) from the Investigation on the Duration of Extended Adjuvant Letrozole (IDEAL) study, sought to determine the ability of BCI to predict the net benefit from 2.5 years vs 5 years of extended endocrine therapy. These data suggest patients should consider extended endocrine therapy if they have a high HOXB13/IL17BR (H/I) ratio, and they confirm that there is a significant net treatment benefit from extended endocrine therapy for patients even when balanced against more serious adverse events (ie, grade 3 or higher).
Biomarkers Independently Contribute to Ability to Predict Extended Endocrine Therapy Benefit
While clinical and pathologic factors are prognostic, they do not reliably predict benefit from extended endocrine therapy. The Molecular Grade Index (MGI) study assessed the relationship of proliferation (MGI) and endocrine response (H/I) to further support how the BCI assay works (Abstract PD9-09). These data confirmed that the two biomarkers contributing to BCI’s risk assessment (H/I and MGI) drove tumor biology, thus validating the assay’s role in offering personalized extended endocrine therapy decisions based on the individual patient’s tumor.
“These data analyzing H/I and MGI genes solidify our understanding of the relationship between these two critical components of BCI,” said study author Reshma Mahtani, DO, Professor of Medicine at the University of Miami’s Sylvester Comprehensive Cancer Center. “The insights confirm H/I and MGI are interdependent contributors of risk and benefit, thus both necessary elements working in combination to determine risk of recurrence in hormone receptor–positive breast cancer.”
