BRAF RNA is prognostic and widely expressed in lung adenocarcinoma

BRAF is a critical member of proliferation pathways in cancer, and a mutation is present in only 2-4% of lung adenocarcinomas (LADC). There is no data available on the expression pattern of BRAF RNA that might result in enhanced signalling and drug resistance.

We found an increased expression of BRAF RNA in all stages in LADC. High BRAF expression was associated with tumor necrosis, distinct immune checkpoint biology and outcomes. We recommend further evaluating the potential of targeting overexpressed BRAF pathways in LADC.

LADC tissue samples (n=64) were fixed and processed into paraffin blocks. Tissue microarrays (TMA) were constructed, and RNAScope® in situ hybridization (ISH) assay was performed for wild-type (WT) BRAF RNA. Apart from pathological assessment of tumor samples (grade, necrosis, vascular involvement and peritumoral infiltration), anti-programmed death ligand 1 (PD-L1) and anti-programmed death 1 (PD-1) immunohistochemistry and validation in public databases [The Cancer Genome Atlas (TCGA), Human Protein Atlas (HPA)] were carried out.

WT BRAF RNA is expressed in LADC, with no significant expressional difference between early-stage (I-II) and advanced-stage (III-IV) patients (P=0.317). Never smokers exhibited significantly increased BRAF expression (compared to current and ex-smokers, P<0.01) and tumor necrosis correlated significantly with BRAF expression (P=0.014). PD-L1 expression was assessed on tumor cells and immune cells, PD-1 expression was evaluated on immune cells. There was no significant difference in BRAF RNA expression between tumor cell PD-L1-high vs. low patients (P=0.124), but it was decreased in immune cell PD-L1-high patients (P=0.03). Kaplan-Meier survival analysis showed that high BRAF expression was associated with significantly decreased OS (P<0.01) and was an independent negative prognostic factor according to multivariate Cox hazard regression (P=0.024). TCGA validation cohort confirmed our findings regarding OS in early-stage patients (P=0.034). Conclusions: We found an increased expression of BRAF RNA in all stages in LADC. High BRAF expression was associated with tumor necrosis, distinct immune checkpoint biology and outcomes. We recommend further evaluating the potential of targeting overexpressed BRAF pathways in LADC.