# Breast Cancer Index

Source: https://onco.cc/drugs/breast-cancer-index/  
OnCo record `breast-cancer-index` (Treatment). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

The only test designed to tell a woman who has finished five years of hormone therapy whether another five years is worth the side effects.

## Summary

Breast Cancer Index (Biotheranostics, acquired by Hologic in 2021) is a laboratory-developed test for hormone-receptor-positive early breast cancer. Its HOXB13:IL17BR component was shown to predict benefit from extending endocrine therapy to 10 years in the MA.17, Trans-aTTom and IDEAL trial cohorts, and the ASCO and NCCN guidelines list it as the test for that decision; a prespecified NSABP B-42 analysis was less clear-cut. It also gives a late-recurrence risk (years 5 to 10). Medicare covers it. The test does not address the initial chemotherapy decision, which is the province of Oncotype DX, MammaPrint, Prosigna and EndoPredict.

## Fields

- Kind: Treatment
- Status: established
- Last checked: 2026-09-10
- Tags: test
- Brand: Breast Cancer Index (BCI)
- Modality: Gene-expression prognostic and predictive assay (extended endocrine therapy benefit)
- Mechanism: RT-PCR combining the HOXB13:IL17BR ratio (predicts benefit from extended endocrine therapy) with the Molecular Grade Index (prognosis for late recurrence).

## Notes

- What a result means: 'BCI (H/I) high' predicts that continuing hormone therapy past five years reduces recurrence; 'low' means the extra years add side effects without measurable benefit.

## Sources

- Breast Cancer Index: https://www.breastcancerindex.com
- ASCO biomarker guideline update (2022): https://doi.org/10.1200/JCO.22.00069

## Connected records

- drugs: [EndoPredict](https://onco.cc/drugs/endopredict/), [Oncotype DX](https://onco.cc/drugs/oncotype-dx/)
- cancers: [HR-positive / HER2-negative breast cancer](https://onco.cc/cancers/breast-hr-positive/)
- technologies: [Endocrine therapy (SERMs, AIs, SERDs)](https://onco.cc/technologies/endocrine-therapy/), [RNA sequencing & expression profiling](https://onco.cc/technologies/rna-seq/)
- companies: [Hologic](https://onco.cc/companies/hologic/)
- key papers: [Biomarkers for Adjuvant Endocrine and Chemotherapy in Early-Stage Breast Cancer: ASCO Guideline Update](https://onco.cc/key-papers/paper-andre-j-clin-oncol/)
- roadmaps: [Hormonal therapy roadmap: removing the ovaries → tamoxifen → oral degraders switched by a blood test](https://onco.cc/roadmaps/hormonal-therapy-roadmap/)
- targets: [HOXB13](https://onco.cc/targets/hoxb13/)

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JSON: https://onco.cc/api/v1/entities/breast-cancer-index.json