A genomic test is reshaping how doctors treat early-stage breast cancer

A large registry study published in JAMA Network Open shows that the Breast Cancer Index (BCI) genomic assay is meaningfully shifting how oncologists approach extended endocrine therapy for women with early-stage, hormone receptor-positive breast cancer. Analyzing data from nearly 3,000 patients across 112 U.S. clinics, researchers found that BCI results led more than 41% of physicians to change their treatment recommendations — and boosted high physician confidence in those decisions from 64% to nearly 89%.

The BCI test delivers two key insights: a prognostic score estimating the risk of cancer returning between years 5 and 10, and a predictive score indicating whether a patient is likely to benefit from continued endocrine therapy. With over 82% of patients reporting side effects from endocrine therapy — including joint pain, hot flashes, and psychological symptoms — the ability to identify who truly needs extended treatment is critical.

By the Numbers:

• 41.7% of physicians changed their recommendations after BCI testing
• Physician confidence rose from 64.1% → 88.7%
• Recommendations for extended therapy dropped from 55.4% → 42.6% overall
• 51% of patients changed their treatment preference post-testing
• 46.5% of women were identified as low-risk for distant recurrence

Why it matters: BCI has the potential to reduce both overtreatment and undertreatment in breast cancer survivorship care — sparing low-risk patients unnecessary side effects while ensuring high-risk patients stay on life-saving therapy. As the survivor population grows faster than the oncology workforce, tools like BCI could play a key role in personalized, risk-stratified care.