Breast Cancer Index Testing Resulted in Changes to Extended Endocrine Recommendations

Physicians changed their extended endocrine therapy (EET) recommendation for 41.7% of patients with early-stage, hormone receptor–positive (HR+) breast cancer after receiving Breast Cancer Index (BCI) results, according to a cohort study from the BCI Registry published in JAMA Network Open.

The BCI gene expression assay, performed by Biotheranostics, provides a prognostic score for risk of late distant recurrence and a predictive component, the HOXB13/IL17BR (H/I) ratio, that classifies patients as having a low or high likelihood of EET benefit. The US multicenter registry enrolled women with stage I to III HR+ breast cancer who remained recurrence free after 4 to 7 years of adjuvant endocrine therapy at 112 clinics from April 2021 to January 2024. Physicians and patients completed questionnaires before and after BCI testing.

The analysis included 2900 women (mean age, 65.2 years). Overall, physician recommendations for EET decreased from 55.4% before testing to 42.6% after testing, and 51.0% of patients changed their preference for EET (both P < .001). Among 1100 patients classified as BCI (H/I)–High, EET recommendations increased from 61.0% to 92.2%. Among 1800 patients classified as BCI (H/I)–Low, recommendations against EET increased from 47.6% to 87.6%.

Physician confidence in the recommendation increased for 43.8% of patients, and 43.4% of patients reported greater comfort with the EET decision. After testing, more patients reported less concern about EET cost, drug safety, and benefit, while concerns about adverse effects remained largely unchanged, the authors reported.

The authors concluded that the study confirms the clinical utility of BCI to support EET decision-making. They noted that self-reported, subjective questionnaire items may introduce bias, that stated preferences may not reflect actual behavior, and that physicians' familiarity with genomic testing may introduce selection bias. Patient follow-up is ongoing.

Source: Sanft TB, Siuliukina N, O'Neal B, et al. Breast Cancer Index and recommendations for extended endocrine therapy. JAMA Netw Open. 2026;9(9):e2634974. doi:10.1001/jamanetworkopen.2026.34974