Gene Expression Profile of Breast Cancer with Monoallelic Somatic <em>BRCA1</em> Inactivation

Background and Objectives: Most of the research of the BRCA1 inactivation is focused on monoallelic germline alterations and loss of heterozygosity in tumour. The aim of this study was to identify characteristic transcriptomic pattern of monoallelic somatic BRCA1 inactivation and estimate its impact to the event-free breast cancer survival prognosis. Materials and Methods: We conducted global transcriptome sequencing of breast cancer tissue samples to identify differentially expressed genes and signalling pathways associated with monoallelic somatic BRCA1 inactivation. The study group involved 36 patient samples categorized based on BRCA1 inactivation status. Subsequently, the differential gene expression and Kaplan-Meier analyses in the groups with and without monoallelic somatic BRCA1 inactivation were performed. Results: Kaplan-Meier analysis showed tendency for longer event-free survival in patients with monoallelic somatic BRCA1 inactivation, suggesting somatic BRCA1 inactivation is favourable prognostic. Differential gene expression analysis followed by the STRING tool enrichment analysis showed significant enrichment of proteins in the extracellular region and extracellular space. Conclusion: In this study we identified transcriptomic profile of differentially expressed genes TPSD1, FABP4, CARTPT and MMP9 as indicative for homologous recombination impaired tumours with tendency for better therapy results.