New Data Shows Breast Cancer Index Testing Influences Extended Endocrine Therapy Decisions
Hologic, Inc. and its subsidiary Biotheranostics, Inc. have announced new findings from the Breast Cancer Index (BCI) Registry Study, showing that use of the genomic test resulted in changes to physicians’ recommendations for extended endocrine therapy (EET) in 41.7% of patients with early-stage, hormone receptor-positive (HR+) breast cancer. The findings were published online September 24, 2026, in JAMA Network Open. (JAMA Network)
The final analysis included 2,900 women who had completed both physician and patient questionnaires before and after receiving BCI testing. Following availability of the BCI results, physicians changed their EET recommendation for 1,209 patients, representing 41.7% of the study population. Patient preferences also changed substantially, with 1,479 patients, or 51.0%, reporting a change in their preference regarding extended endocrine therapy. (JAMA Network)
The study evaluated patients enrolled across 112 clinics in the United States between April 2021 and January 2024. Participants had early-stage HR-positive breast cancer and had remained recurrence-free after approximately four to seven years of primary adjuvant endocrine therapy. The registry was designed to examine how BCI results influence treatment decisions, patient preferences and confidence surrounding the decision to continue endocrine therapy beyond the initial treatment period. (JAMA Network)
Extended Endocrine Therapy Can Present a Complex Treatment Decision
Endocrine therapy is an important component of treatment for many patients with hormone receptor-positive breast cancer because it can reduce the risk of recurrence associated with hormone-driven tumor growth. However, continuing treatment beyond the initial five-year period can involve a complex assessment of potential benefits and treatment-related adverse effects.
The decision is particularly relevant because hormone receptor-positive breast cancer can recur many years after the initial diagnosis. At the same time, not every patient receives the same degree of benefit from extended endocrine therapy, while continued treatment can contribute to adverse effects that affect quality of life and adherence.
The BCI Registry Study examined this clinical decision in patients who had already completed several years of endocrine treatment. The study found that physicians’ recommendations changed substantially after they received the genomic test results, suggesting that molecular information could add another layer of individualized information beyond conventional clinicopathologic factors.
Tara B. Sanft, M.D., of Hartford Healthcare Cancer Institute and lead author of the study, said decisions regarding extended endocrine therapy can be challenging when clinicians rely on standard clinical information such as tumor size and lymph-node involvement.
“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,” Sanft said.
BCI Results Changed Treatment Recommendations
The final registry analysis showed that BCI testing affected recommendations in both directions. Overall, the number of physicians recommending extended endocrine therapy declined from 1,606 before testing to 1,234 after BCI results were available. Conversely, the number of physicians recommending against extended endocrine therapy increased from 1,281 before testing to 1,655 following testing. (JAMA Network)
The changes were closely associated with the predictive component of the BCI test, which evaluates the likelihood that a patient will benefit from extended endocrine therapy.
Among the 1,100 patients classified as BCI (H/I)-High, indicating a higher likelihood of benefit, the number of physicians recommending extended endocrine therapy increased from 671 before testing to 1,014 after testing. That represented an increase from 61.0% to 92.2% of patients in that subgroup. (JAMA Network)
In contrast, among the 1,800 patients classified as BCI (H/I)-Low, indicating a lower likelihood of benefit, physicians recommending against extended endocrine therapy increased from 856 before testing to 1,576 after receiving the results. The proportion increased from 47.6% to 87.6%. (JAMA Network)
These results demonstrate how the BCI predictive result was incorporated into treatment recommendations in the real-world registry population. The study was observational and evaluated changes in physician recommendations after testing rather than randomly assigning patients to treatment strategies.
Patients Reported Substantial Endocrine Therapy Side Effects
Treatment tolerability was another important factor examined in the registry. Of the 2,900 women included in the final analysis, 2,399, or 82.7%, reported adverse effects associated with endocrine therapy at baseline. (JAMA Network)
The most frequently reported complaints included muscle and joint symptoms, hot flashes, vaginal symptoms, psychological complaints and sexual symptoms. Muscle and joint complaints were reported by 61.5% of patients, while 59.9% reported hot flashes. Vaginal complaints were reported by 40.4%, psychological complaints by 38.7% and sexual complaints by 35.9%. (JAMA Network)
Although most reported adverse effects were mild or moderate, 717 patients, or 24.7%, reported at least one severe adverse effect. Muscle and joint complaints and hot flashes were the most frequently reported symptoms classified as moderate or severe. (JAMA Network)
These findings provide context for why individualized decisions around treatment duration can be important. Continuing endocrine therapy may provide additional protection against recurrence for some patients, but the potential benefits must be considered alongside treatment tolerability and individual risk.
BCI Provides Prognostic and Predictive Information
The Breast Cancer Index is a gene-expression assay that provides both prognostic and predictive information. According to the published study, the prognostic component evaluates the risk of overall and late distant recurrence, while the predictive component uses the HOXB13/IL17BR, or H/I, ratio to assess the likelihood of benefit from extended endocrine therapy. (JAMA Network)
Within the final cohort, 1,348 patients, or 46.5%, were classified as having a low risk of late distant recurrence, while 1,552 patients, or 53.5%, were classified as having a high risk. The predictive component categorized 1,800 patients, or 62.1%, as BCI (H/I)-Low and 1,100 patients, or 37.9%, as BCI (H/I)-High. (JAMA Network)
The distinction between prognostic and predictive information is relevant to treatment planning. A prognostic result provides information about recurrence risk, while a predictive result is intended to provide information about the potential benefit of a particular treatment strategy.
For extended endocrine therapy, this distinction can help clinicians consider not only whether a patient has a risk of late recurrence but also whether continuing endocrine treatment is likely to provide meaningful benefit.
Physician Confidence Also Increased
The study examined not only whether recommendations changed but also physicians’ confidence in their treatment decisions.
Following BCI testing, physician confidence increased for 1,269 patients, representing 43.8% of the cohort. The study reported that this increase was statistically significant. Patient comfort with the treatment decision also increased for 1,260 patients, or 43.4%. (JAMA Network)
The results indicate that genomic information may influence the decision-making process beyond simply changing the direction of a treatment recommendation. It may also provide clinicians and patients with additional information when discussing the advantages and disadvantages of continued endocrine therapy.
Patient preferences changed in 51.0% of the cohort after BCI testing. The direction of those changes varied according to the patient’s BCI category and likelihood of benefit. (JAMA Network)
BCI Registry Provides Real-World Clinical Evidence
The BCI Registry is a prospective, multicenter US study evaluating long-term clinical outcomes, treatment decision-making and medication adherence among patients with early-stage HR-positive breast cancer.
The registry enrolled approximately 3,000 women at 112 US clinics. For the analysis published in JAMA Network Open, 3,023 patients had been enrolled, 2,977 had verified clinical information and BCI testing results, and 2,900 had completed the physician and patient questionnaires both before and after testing. (JAMA Network)
The average age of the final cohort was 65.2 years. Most participants were postmenopausal, with 88.6% in that category. Approximately 77.4% had node-negative disease, 86.2% had HER2-negative tumors and 73.4% had T1 tumors. Nearly two-thirds of participants had not received chemotherapy. (JAMA Network)
The study’s patient follow-up remains ongoing, with completion anticipated in 2028. Therefore, the currently published analysis focuses on treatment decision impact and related measures rather than providing the final long-term clinical outcome results of the entire registry. (JAMA Network)
Updated BCI Reporting Expands Information Available at Diagnosis
Hologic and Biotheranostics have also highlighted an updated reporting option for the BCI test introduced in July 2026. The companies said the updated report provides additional clinical information earlier in the treatment journey, including context around 10-year recurrence risk.
The companies’ stated goal is to help physicians and patients incorporate recurrence-risk information into treatment planning from the time of diagnosis, rather than limiting the value of the test to decisions about extended endocrine therapy several years after initial treatment.
Lloyd Sanders, vice president and general manager of Oncology Services at Hologic, said the updated report is intended to help physicians and patients develop a more individualized long-term treatment plan.
“The Breast Cancer Index test’s updated report supports a more informed plan for the years ahead,” Sanders said, adding that it is intended to provide additional clarity as patients plan treatment and survivorship.
Role in Personalized Breast Cancer Care
The findings add to the body of evidence surrounding genomic testing in hormone receptor-positive breast cancer. The BCI test has been recognized in the National Comprehensive Cancer Network and American Society of Clinical Oncology clinical practice guidelines for decision-making regarding extended endocrine therapy. (JAMA Network)
Hologic and Biotheranostics said the test has been used by more than 10,000 healthcare providers and evaluated in clinical studies involving more than 15,000 patients.
The newly published registry findings provide evidence from a large, multicenter real-world cohort showing that BCI results can influence treatment recommendations, patient preferences and confidence in decisions about extended endocrine therapy.
For patients with HR-positive breast cancer, the decision to continue endocrine treatment after the initial treatment period involves balancing recurrence risk, expected treatment benefit, adverse effects, patient preferences and other clinical considerations. The BCI Registry findings suggest that genomic information can alter how physicians and patients weigh those factors.
The study does not establish that BCI testing itself improves survival or reduces recurrence; rather, it demonstrates changes in treatment recommendations and decision-related measures after test results were available. Long-term follow-up of the registry is continuing.
As the management of early-stage breast cancer increasingly incorporates individualized tumor biology alongside traditional clinical characteristics, Hologic and Biotheranostics are positioning the BCI test as a tool for supporting treatment decisions across the breast cancer care pathway. The latest JAMA Network Open findings provide additional evidence on how the test is being used in clinical practice, particularly when physicians and patients must decide whether the potential benefits of extended endocrine therapy justify continued treatment. (JAMA Network)
About the Breast Cancer Index Test
The Breast Cancer Index test is a molecular, gene expression-based test uniquely positioned to provide information to help physicians individualize treatment decisions for patients with early-stage, HR+ breast cancer. This breakthrough test helps oncology care teams 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.
The Breast Cancer Index test has guideline designation from the American Joint Committee on Cancer for cancer staging based on molecular profile. The ASCO® Clinical Practice Guideline and the NCCN Guidelines® acknowledge the Breast Cancer Index test as a biomarker to help inform extended endocrine treatment decisions.2-3
The Breast Cancer Index test is intended for routine clinical use, and physician treatment decisions based on results are the responsibility of the physician. It is a sole-source laboratory-developed test (LDT) performed by Biotheranostics, Inc., a CLIA-certified and CAP-accredited diagnostic laboratory. For more information and the full intended use and limitations, visit www.breastcancerindex.com.
About Hologic, Inc.
Hologic, Inc. is a global leader in women’s health dedicated to developing innovative medical technologies that effectively detect, diagnose and treat health conditions and raise the standard of care around the world.