# Radiotherapy in breast cancer brain metastases: the impact of time interval and disease dynamics when breast cancer seeds to the brain

## TL;DR

This study examines how quickly breast cancer spreads to the brain and how this speed affects survival, finding that disease dynamics and biological subtypes are important factors.

## Contribution

The study extends the use of initial brain metastasis velocity (iBMV) to breast cancer brain metastases and identifies its prognostic value in mixed radiotherapy settings.

## Key findings

- iBMV independently predicts mortality in breast cancer brain metastases patients.
- Biological subtypes significantly influence the time interval between initial diagnosis and brain metastasis occurrence.
- Karnofsky performance status and HER2 status are the strongest predictors of overall survival.

## Abstract

The initial brain metastasis velocity (iBMV) is a prognostic metric introduced for patients receiving stereotactic radiosurgery (SRS) for brain metastases (BM), reflecting intracranial disease dynamics. This study aimed to assess the applicability of iBMV in a mixed cohort of breast cancer brain metastases (BCBM) patients treated with SRS/fractionated stereotactic radiotherapy (FSRT) and whole-brain radiotherapy (WBRT). Considering disease dynamics, we analyzed the role of biological subtypes in determining the time interval between initial diagnosis and the occurrence of BM.

We conducted a retrospective, single center cohort study of 126 BCBM patients who received radiotherapy to the brain (SRS/FSRT and WBRT) between 01/2013 and 12/2020. Statistical endpoints included iBMV, time interval between initial diagnosis and the occurrence of BM analyzed per biological subtype, and overall survival (OS).

Median iBMV was 0.48 BM/year. The iBMV independently predicted for mortality in the multivariate model after accounting for WBRT (hazard ratio [HR] = 1.21; 95% confidence interval [CI] 1.04–1.41; p = 0.012). The biologic subtype significantly influenced the time interval between initial diagnosis of breast cancer and occurrence of BM. In a multivariate model, the Karnofsky performance status and HER2 status were strongest predictors of overall survival (HR = 2.60; 95% CI 1.60–4.22; p < 0.001 and HR = 2.26; 95% CI 1.34–3.84; p = 0.002, respectively).

iBMV correlates with overall survival, regardless of whether WBRT was used as part of local treatment. The biological subtype has a profound impact on prognosis and kinetics of BCBM.