Could a Genomic Test Spare You Extra Years of Hormone Therapy?

Results from the Breast Cancer Index (BCI) test led physicians to change their recommendations about extended endocrine therapy for 42% of patients with early-stage hormone receptor (HR)-positive breast cancer, according to findings published in JAMA Network Open.

In two-thirds of those cases, physicians changed their recommendation against extending treatment beyond the standard course.

How Did the Breast Cancer Index Test Change Treatment Recommendations?

The findings come from the final analysis of the BCI Registry Study, which looked at how physicians used BCI test results when deciding whether to recommend extended endocrine therapy.

After reviewing test results, physicians changed their recommendation for 42% of patients. Most of those changes moved away from extended treatment, meaning some patients could potentially avoid additional years of therapy and its side effects.

Lead study author Dr. Tara B. Sanft, of Hartford HealthCare, said in a news release that decisions about extended endocrine therapy can be difficult, and that relying only on standard clinical factors — such as whether the cancer has spread to lymph nodes and the tumor's size and grade — can be misleading. She added that the test offers "individualized insight into tumor biology" that can meaningfully shift how physicians and patients approach these decisions.

What Is the Breast Cancer Index Test?

The BCI test is a molecular, gene expression-based test designed to help physicians tailor treatment decisions for people with early-stage HR-positive breast cancer. It is recognized by both the National Comprehensive Cancer Network (NCCN) guidelines and the American Society of Clinical Oncology (ASCO) clinical practice guideline as a genomic test that predicts which patients with early-stage HR-positive, HER2-negative breast cancer are likely to benefit from extended endocrine therapy.

As of July 2026, physicians can also access an updated report option from the same test that provides insight at the time of diagnosis. The updated report includes context on 10-year recurrence risk, which may either support staying on treatment or help identify whether a patient's risk is low enough to consider a less intensive approach.

Who Was Included in the BCI Registry Study?

The registry study was conducted across multiple institutions at Sarah Cannon Research Institute and included nearly 3,000 patients with early-stage HR-positive breast cancer who received the BCI test.

Extended endocrine therapy decisions matter because approximately half of recurrences in HR-positive breast cancer occur more than five years after diagnosis. Multiple trials have shown that while extending endocrine therapy may lower the risk of late recurrence for some women, not everyone benefits.

What Side Effects Did Patients Report From Endocrine Therapy?

In this analysis, 83% of patients reported side effects from endocrine therapy, including muscle and joint pain as well as vaginal, sexual and psychological concerns.

Endocrine therapy, which helps limit the effects of hormones that can fuel cancer growth, is often the longest phase of treatment for people with breast cancer. Research suggests roughly 30% to 50% of women stop endocrine therapy before reaching the five-year mark, often because of side effects or uncertainty about whether continuing treatment is necessary.

References:

• New Data Shows Physicians Changed Extended Endocrine Therapy Recommendations for Over 40% of Patients Following Breast Cancer Index Testing (Business Wire via Yahoo Finance)
• Sanft T, et al. JAMA Netw Open. 2026;9(9):e2634974

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