BTN2A1-BRAF fusion may be a novel mechanism of resistance to osimertinib in lung adenocarcinoma: a case report.

BACKGROUND: Non-small cell lung cancer (NSCLC) is one of the most common malignancies in the world. Osimertinib is a third-generation epidermal growth factor receptor tyrosine kinase inhibitor ( EGFR -TKI) indicated for NSCLC that effectively targets sensitive epidermal growth factor receptor mutation and exon20 T790M. Despite initially impressive outcomes, acquired resistance (AR) develops rapidly, typically within 9-13 months, and the mechanisms of resistance are not fully understood. Over the past years, EGFR -TKI and programmed cell death-ligand 1 (PD-L1) inhibitors have been widely used to treat for patients with advanced lung adenocarcinoma.

CASE DESCRIPTION: Herein we report a middle-aged female who suffered from lung adenocarcinoma based on the pathological diagnosis. Epidermal growth factor receptor exon 19 deletion was detected by next-generation sequencing (NGS). After the patient underwent a series of treatments, including osimertinib, BTN2A1-BRAF fusion was identified. After assessing PD-L1 expression by immunohistochemistry (IHC), the patient was switched to duvalizumab, a PD-L1 inhibitor, but no significant improvements were observed. NGS and IHC assays were conducted to analyze the biopsy and blood samples obtained during treatment.

CONCLUSIONS: This case substantiates that the acquisition of BTN2A1-BRAF fusion potentially serves as a mechanism of AR to osimertinib in NSCLC. Patients with sensitive epidermal growth factor receptor mutation derive minimal benefit from PD-L1 inhibitors irrespective of the degree of PD-L1 expression in the tumor tissue in IHC. Our case provides a new train of thought for treating this patient population.