Cytomegalovirus viremia and hepatitis B reactivation in patient with RET fusion-positive non-small cell lung cancer treated with pralsetinib.

Introduction: Mutated rearranged during transfection (RET) kinase is found in approximately 1-2% non-small-cell lung cancer (NSCLC) patients. These patients are typically younger, non-smokers, and have non-squamous histology. Pralsetinib is a novel RET inhibitor that showed promising efficacy and tolerability in the ARROW trial. Due to the small percentage of patients that have RET mutated NSCLC, real world data on safety is still needed.

Case report: This case report outlines a patient who was initiated on pralsetinib for RET mutated NSCLC and subsequently developed reactivation of cytomegalovirus (CMV) viremia and hepatitis B.

Management and outcome: The patient was initiated on valganciclovir and entecavir with subsequent improvement in viral loads. They were able to reinitiate pralsetinib at a lower dose following improvement of CMV and hepatitis B viral load with continuation of entecavir.

Discussion: RET is responsible for activation of several signaling paths including PI3K/AKT and JAK/STAT. Those pathways are involved in the immune system. When reviewing current JAK inhibitors and PI3K inhibitors on the market, there is mixed data on HBV reactivation and CMV viremia, though theoretically possible. Therefore, this should be evaluated and addressed in further studies. The educational value of this case could provide valuable insights for baseline monitoring and management for similarly effected patients.