Predicting response to 10 years of endocrine therapy in patients with hormone receptor positive early stage breast cancer

The study evaluated whether Breast Cancer Index (BCI) can predict benefits from extended endocrine therapy (EET) in patients with hormone-receptor-positive (HR+) early-stage breast cancer (BC). The authors found that BCI can predict which patients would benefit from 10 years of EET.

Endocrine therapy (ET) prevents tumor growth in patients with HR+ BC. They normally receive 5-years of adjuvant-ET, which is given to maximize the effects of a primary treatment. Extending such ET to a total of 10-years reduces relapse but causes severe toxicities. It is important to select patients for EET by balancing toxicities versus benefits.

BCI is a genetic test that previously predicted risks of relapse in HR+ BC. Its power to predict benefits from EET is unknown.

The study conducted the BCI test on tumor samples of 908 adult women with early-stage HR+ BC. After completing 5 years of adjuvant-ET, half of the patients received 2.5-years of ET with letrozole (Femara). The other half received 5-years of letrozole (EET group).

47% of patients had high BCI-scores. In these patients, the BCI test predicted 58% higher chances of benefitting from letrozole treatment another 5 years. Risks of relapse were 5.9% for the EET group and 15.7% for patients who received 2.5 years of letrozole. Patients in the EET group had a 9.8% lower risk of recurrence compared to those in the 2.5-year group.

A total of 53% of patients had low BCI scores. Among these patients, the duration of letrozole therapy had no impact on the benefit and risks of relapse. The risk of recurrence was 14.9% with EET and 15.4% in the 2.5-year therapy group.

In patients receiving an aromatase inhibitor (AI) such as letrozole as part of adjuvant-ET, high BCI scores predicted significant benefits from EET. 5-years of letrozole had a 66% higher benefit compared to 2.5-years. 

Among patients with high-risk disease (HRD) and cancer spreading to lymph nodes, 46% had high BCI-scores. 5-years of letrozole had 68% higher chances of a benefit than 2.5-years. 

The study concluded that high BCI scores can predict benefit from 5 versus 2.5 years of letrozole therapy in patients with early-stage HR+ BC. 

This study was based on medical records. Many of the patients were also receiving chemotherapy. This might have influenced the results.