Remarkable response to pralsetinib in an advanced pulmonary sarcomatoid carcinoma patient harboring a KIF5B-RET rearrangement: A case report

Background: Pulmonary sarcomatoid carcinoma (PSC) is a rare and unconventional non-small-cell lung cancer (NSCLC) that appears to be more aggressive, with a poorer prognosis and response to conventional treatment. Approximately 30% of PSCs have potentially targetable genomic alterations, but few studies have involved RET gene fusions, and corresponding targeted therapies are lacking. Case presentation: In this report, we describe a patient with PSC harboring a KIF5B-RET gene fusion who was initially diagnosed with stage IVb lung cancer. Due to the poor performance status, the patient was unable to tolerate any radiotherapy or chemotherapy. Based on the next-generation sequencing (NGS) result of RET gene fusion, the patient was treated with pralsetinib. Two months after the treatment, the patient achieved a partial response. Conclusions Our case indicates that RET is one of the main driver oncogenes of PSC and provides useful information for precise RET inhibitor administration in the future. In addition, this case shows that dynamic NGS tests can assist in clinical decision-making by presenting molecular changes.