New data from the Tamoxifen and Exemestane Trial (TEXT) suggest that the Breast Cancer Index (BCI) may help identify premenopausal patients with hormone receptor–positive (HR+) early breast cancer most likely to benefit from more intensive adjuvant endocrine therapy with exemestane plus ovarian function suppression (OFS).
In this translational analysis, investigators assessed 1,782 women from TEXT (67.0% of the TEXT intention-to-treat population) with a median follow-up of 13 years. Overall, exemestane plus OFS was associated with a 6.4% absolute improvement in 12-year breast cancer–free interval (BCFI) compared with tamoxifen plus OFS (HR 0.69; 95% CI 0.55–0.87).
When stratified by BCI HOXB13/IL17BR (H/I) status:
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Patients with BCI (H/I)–low tumours experienced a 6.6% absolute BCFI benefit (HR 0.61; 95% CI 0.44–0.85).
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Those with BCI (H/I)–high tumours had a 6.3% absolute benefit (HR 0.78; 95% CI 0.57–1.07).
The treatment-by-biomarker interaction was not statistically significant (P = .29), though analyses using BCI as a continuous variable suggested a possible predictive association (P = .04).
In the combined TEXT + SOFT analysis of nearly 2,900 patients, BCI (H/I)–low tumours showed a 5.7% absolute 12-year BCFI benefit (HR 0.65; 95% CI 0.50–0.83), compared with 4.2% in the BCI (H/I)–high group (HR 0.86; 95% CI 0.67–1.09).
Exploratory analyses suggested that treatment effects may differ over time, with greater relative benefit for BCI (H/I)–low tumours in the first 5 years of therapy.
In prognostic analyses among women with node-negative disease, BCI remained significantly associated with distant recurrence risk at 12 years.
While the overall treatment benefit of exemestane + OFS over tamoxifen + OFS was consistent across biomarker groups, these findings suggest that BCI may help refine individualised endocrine therapy decisions for premenopausal women with HR+ early breast cancer.
Paper: O’Regan RM, et al. Assessment of Adjuvant Endocrine Therapy With Ovarian Function Suppression by Breast Cancer Index. JAMA Netw Open. 2025;8(11):e2540931. Access online here.
