Genomic Test Guides Extended Endocrine Therapy in Early Breast Cancer

Adjuvant endocrine therapy is standard for hormone receptor–positive early breast cancer, yet prolonged treatment brings side effects and adherence problems. Whether to continue beyond five years is a common dilemma. A genomic test now helps clinicians tailor extended endocrine therapy decisions using tumor‑specific biology.

Hologic, Inc. and its subsidiary, Biotheranostics, Inc., reported results from the multi‑institution Breast Cancer Index (BCI) Registry Study, published in JAMA Network Open. Among about 3,000 HR‑positive early‑stage patients tested, physicians changed extended endocrine therapy recommendations for 42%. In two‑thirds of those changes, clinicians recommended against extending treatment.

BCI is a gene expression-based assay that provides individualized insight into tumor biology to help guide extended endocrine therapy decisions. The test is recognized in the National Comprehensive Cancer Network (NCCN) Clinical Practice Guidelines in Oncology and the American Society of Clinical Oncology (ASCO) Clinical Practice Guideline as a tool for predicting which patients are likely to benefit from extended therapy. It is performed as a sole-source laboratory-developed test in a CLIA-certified, CAP-accredited laboratory.

In the analysis, 83% of patients reported endocrine‑therapy side effects, including musculoskeletal and psychological complaints. An updated BCI report option, available since July 2026, provides additional insights at diagnosis on 10‑year recurrence risk. These insights can support adherence when risk is higher or suggest when a less intensive endocrine approach may be considered.

“Decisions about extended endocrine therapy can be challenging, and assumptions based on standard information, such as nodal involvement and tumor size and grade, may be misleading,” said Tara B. Sanft, M.D., of Hartford Healthcare and lead author of the study. “This final analysis of the BCI Registry Study reinforces the clinical utility of the Breast Cancer Index test to provide individualized insight into tumor biology that can meaningfully change how physicians and patients approach these decisions.”