Rho-GTPase activating protein 18: a biomarker associated with good prognosis in invasive breast cancer

Background: The prognostic value of lymphovascular invasion (LVI) in breast cancer (BC) has been demonstrated in several independent studies. However, identification of driver molecules for LVI remains a challenging task. Large-scale transcriptomic profiling of histologically validated LVI can potentially identify genes that regulate LVI. Methods:Integrative bio-informatics analyses of the METABRIC study were performed utilising a subset of strictly defined LVI using histological and immunohistochemical (IHC) criteria. ARHGAP18 was amongst the top differentially expressed genes between LVI+ and LVI- BC with a 1.8 fold change. The prognostic impact of ARHGAP18 gene expression was assessed in the METABRIC dataset (n=1980) and externally validated using the online BC gene expression datasets utilising bc-GenExMiner v4.0 (n=2016). Subsequently, ARHGAP18 protein expression was assessed on a large cohort of invasive BC (n=959) with long term follow-up using IHC. Results: Pooled analysis of ARHGAP18 mRNA expression showed that overexpression was associated with better outcome (p