Combined RET and MEK Inhibition as a Treatment for RET Fusion-Positive NSCLC With Acquired BRAF Fusion: A Case Report

RET fusions are present in 1% to 2% of NSCLCs. Although RET inhibitors like selpercatinib are effective, resistance inevitably develops. We present the case of a 28-year-old female with recurrent NSCLC and a CCDC6::RET fusion treated with selpercatinib. Testing at the time of progression revealed a new SKAP2::BRAF fusion. She was then treated with a combination of selpercatinib and trametinib, which led to a likely partial response, despite the combination demonstrating side effects. This case report details the first known instance of NSCLC with a RET fusion developing resistance by means of a BRAF fusion, treated with combined RET and MEK inhibition.