Clinically actionable genomic alterations in breast cancer brain metastases

BACKGROUND: Breast cancer brain metastases (BCBMs) represent a critical unmet clinical need in metastatic breast cancer (MBC) and the identification of novel therapeutic targets is urgently needed in this context. In this study, we describe clinically actionable targets in BCBMs using comprehensive genomic profiling. PATIENTS AND METHODS: Genomic DNA was extracted from formalin-fixed paraffin-embedded archival BCBM samples and analyzed using the commercially available Agilent SureSelect V6 whole exome sequencing (WES) kit and an Illumina NovaSeq 6000 platform. Pathogenic alterations were classified as actionable alterations (AAs) if they met the updated MBC or tumor-agnostic ESMO Scale for Clinical Actionability of Molecular Targets (ESCAT) I or II criteria of the ESCAT scale. RESULTS: WES data from 56 BCBM samples were available [33.9% hormone receptor (HR)-negative/human epidermal growth factor receptor (HER)2-negative; 25.0% HR-positive/HER2-negative; and 38% HER2-positive]. ESCAT I/II AAs were detected in 76.8% (n = 43) of all BCBMs and the most frequently detected AAs were in genes involved in the homologous recombination repair pathway (BRCA1/BRCA2/PALB2; 53.6% overall). Biallelic inactivation of BRCA1, BRCA2, or PALB2 was observed in 19.6% of samples, with higher rates in HER2-negative BCBMs (26% in HR-negative /HER2-negative and 21% in HR-positive/HER2-negative). ESCAT I/II PIK3CA/AKT1/PTEN pathway alterations were present in 48.2% of samples and, in particular, in 50% of HR-positive/HER2-negative BCBMs. No ESR1 mutation was detected in HR-positive/HER2-negative BCBMs. The prognostic impact of previously described AAs was evaluated overall and according to breast cancer subtype. Twenty-three BCBMs (41%) were classified as HER2-positive; among these, 3 (13%) presented a hotspot PIK3CA mutation and 7 (30%) presented a PTEN deletion. Among patients with HER2-positive BCBMs, the identification of a hotspot PIK3CA mutation was significantly associated with worse prognosis. CONCLUSIONS: ESCAT I/II actionable genomic alterations are frequent in BCBMs, highlighting the potential for genomically targeted treatments in this setting.