RESEARCH has shown that the Breast Cancer Index (BCI) can effectively prognosticate outcomes and predict the benefit of ovarian function suppression (OFS)–based adjuvant endocrine therapy in premenopausal women with hormone receptor-positive (HR+) breast cancer. Specifically, BCI HOXB13/IL17BR ratio (BCI[H/I])-low tumours are associated with greater benefit from this therapy compared to BCI(H/I)-high tumours.
This study aimed to assess the predictive and prognostic performance of BCI in guiding OFS-based adjuvant endocrine therapy in premenopausal women with HR+ breast cancer. Conducted as a prospective-retrospective translational study, it involved analysing tumour tissue samples from 1,687 patients enrolled in the Suppression of Ovarian Function Trial (SOFT). These patients were randomised to receive either tamoxifen alone, tamoxifen plus OFS, or exemestane plus OFS over five years. BCI testing was performed blindly, with the hypothesis that patients with BCI(H/I)-high tumours would derive greater benefit from OFS, and a higher BCI continuous index would be linked to poorer prognosis.
The results demonstrated that patients with BCI(H/I)-low tumours experienced a significant benefit from OFS-based therapies. Specifically, a 12-year follow-up revealed that patients with BCI(H/I)-low tumours had an 11.6% absolute improvement in breast cancer–free interval (BCFI) when treated with exemestane plus OFS and a 7.3% improvement with tamoxifen plus OFS, compared to tamoxifen alone. In contrast, BCI(H/I)-high tumours did not benefit from the addition of OFS to tamoxifen or exemestane. Additionally, the BCI continuous index was a significant prognostic marker for distant recurrence-free interval (DRFI) in node-negative (N0) patients, with poorer outcomes observed in those with higher BCI scores.
The findings suggest that BCI, particularly the BCI(H/I) ratio, could be a valuable tool in clinical practice for identifying premenopausal women with HR+ breast cancer who are most likely to benefit from OFS-based adjuvant endocrine therapy. Further validation studies are necessary to confirm these results and solidify the role of BCI in personalising treatment plans, potentially leading to more effective and tailored therapy with minimised adverse effects.
Katrina Thornber, EMJ
Reference
O’Regan RM et al. Breast cancer index in premenopausal women with early-stage hormone receptor-positive breast cancer. JAMA Oncol. 2024;DOI:10.1001/jamaoncol.2024.3044.
