# Mutational Landscape Analysis of BRCA1/2 and Identification of Extracellular-Vesicle-Related Biomarkers in Triple-Negative Breast Cancer

## TL;DR

This study analyzes BRCA1/2 mutations and identifies PLA2G5 as a potential biomarker and drug target for triple-negative breast cancer.

## Contribution

The study identifies PLA2G5 as a novel EV-related biomarker and drug target for TNBC treatment.

## Key findings

- PLA2G5 is significantly downregulated in TNBC and is enriched in drug metabolism pathways.
- Leukotriene C4 showed high binding affinity to PLA2G5, suggesting potential therapeutic use.
- Differences in immune cell expression were observed between BRCA1/2 mutation and wild-type groups.

## Abstract

Background: Triple-negative breast cancer (TNBC), defined by the absence of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER-2) expression, is associated with increased BRCA1/2 mutation rates. Extracellular vesicles (EVs) play a pivotal role in TNBC progression. This study aimed to analyze BRCA1/2 mutations and identify EV-related biomarkers for TNBC by employing TNBC-related datasets and EV-related genes (EVRGs). Methods: Initially, BRCA1/2 mutations in TNBC patients were examined. Differentially expressed EVRGs (DE-EVRGs) were identified by integrating the results of both differential expression analysis and weighted gene co-expression network analysis (WGCNA). Biomarkers were identified using Receiver Operating Characteristic (ROC) and Kaplan–Meier (K–M) analyses. Finally, functional enrichment, drug prediction, molecular docking, and reverse transcription quantitative polymerase chain reaction (RT-qPCR) analyses were performed. Results: Waterfall plots indicated that TP53 exhibited the highest mutation frequency in both the mutation (MUT) and wild-type (WT) group. Four distinct types of immune cells (for example, eosinophils and neutrophils) showed significantly elevated expression levels in the WT group. Notably, PLA2G5 was identified as a biomarker of TNBC and its expression was significantly lower in TNBC (p = 0.0025). Functional analysis demonstrated that PLA2G5 is enriched in the “drug metabolism cytochrome P450” pathway. Finally, 20 drugs targeting PLA2G5 were identified, among which leukotriene C4 demonstrated a binding affinity of −7.2 kcal/mol. This finding suggests that leukotriene C4 has potential therapeutic applications for the treatment of TNBC. Conclusions: Our study found significant differences between the MUT and WT groups, identifying PLA2G5 as a biomarker for TNBC and offering a theoretical basis for TNBC treatment.