From: oncodaily.com
Brain metastases remain one of the most difficult complications of metastatic breast cancer. Approximately 30% of patients with metastatic disease will eventually develop central nervous system involvement, and despite major improvements in systemic therapy, CNS progression continues to influence survival, quality of life, and treatment sequencing.
A 2026 study published in ESMO Open now adds another dimension to this challenge: breast cancer brain metastases may contain a substantial number of clinically actionable genomic alterations that are not necessarily captured by profiling the primary tumor or extracranial disease.
Griguolo, Collesei and colleagues performed comprehensive genomic profiling of surgically resected breast cancer brain metastases and found ESCAT I/II actionable alterations in 76.8% of samples. Alterations involving homologous recombination repair and the PI3K/AKT/PTEN pathway were particularly frequent, suggesting that the biology of CNS disease may contain therapeutic vulnerabilities that deserve specific attention.
The study does not establish that genomic sequencing of brain metastases should immediately dictate treatment. No patient received therapy based on the sequencing results, and prospective evidence demonstrating benefit from CNS genotype–matched treatment remains limited. But the findings raise an increasingly relevant question for precision breast oncology:
Are we adequately characterizing the tumor that is actually growing in the brain?
Brain Metastases May Not Be Genomically Equivalent to the Primary Tumor
The traditional approach to metastatic breast cancer often relies on molecular information obtained from the primary tumor or an extracranial metastatic biopsy. That approach assumes sufficient biological continuity across different disease sites. Brain metastases challenge that assumption.
Previous studies have documented discordance in hormone receptor and HER2 status between primary breast tumors and matched brain metastases, with reported discordance rates of approximately 21% for hormone receptors and 10% for HER2. Molecular evolution during CNS dissemination can extend beyond receptor status, producing changes in gene expression and potentially actionable genomic alterations.
The brain is not simply another metastatic site. Tumor cells reaching the CNS must adapt to a distinct microenvironment, overcome or exploit the blood–brain barrier, and interact with neural and immune components that differ substantially from those present in extracranial organs.
This evolutionary pressure may create or select molecular features that are particularly relevant to CNS disease.
The Study Focused on Clinically Actionable Alterations
The investigators retrospectively identified patients with breast cancer who underwent neurosurgery at three institutions between 2003 and 2019. Among 88 archived brain metastasis samples, 56 had sufficient material for genomic analysis. Whole-exome sequencing was performed using the Agilent SureSelect V6 platform, and genomic alterations were classified according to the updated ESMO Scale for Clinical Actionability of Molecular Targets (ESCAT).
Only alterations meeting ESCAT level I or II criteria for metastatic breast cancer or tumor-agnostic indications were considered clinically actionable. The 56 brain metastases represented several biologically distinct populations: 33.9% were HR-negative/HER2-negative, 25.0% were HR-positive/HER2-negative, and 38% were HER2-positive.
Most patients had a single brain metastasis, reflecting an important characteristic of the cohort: these were patients selected for neurosurgical resection rather than an unselected population with CNS metastatic disease.
More Than Three-Quarters of Brain Metastases Had an ESCAT I/II Alteration
The headline result was the high prevalence of potentially actionable molecular findings. Among the 56 evaluable brain metastases, 43 tumors—76.8%—contained at least one ESCAT I/II actionable alteration.
The frequency remained high across breast cancer subtypes:
- 85.7% in HR-positive/HER2-negative disease, 68.4% in HR-negative/HER2-negative disease, and
- 78.3% in HER2-positive disease.
This does not mean that three-quarters of patients currently have an approved CNS-active targeted treatment available. Actionability according to ESCAT describes the strength of evidence linking an alteration to a therapeutic strategy. In brain metastases, another critical variable must be added: can the relevant drug achieve sufficient intracranial exposure to exploit that target?
The study therefore identifies therapeutic opportunities rather than demonstrating therapeutic benefit.
Barbara Jacoby is an award winning blogger that has contributed her writings to multiple online publications that have touched readers worldwide.