Chylous Ascites, a Rare Adverse Reaction to Selpercatinib

Selpercatinib improves outcomes in Rearranged during Transfection (RET) fusion-positive non-small cell lung cancer (NSCLC) but can rarely cause chylous ascites (CA). We report the case of a 53-year-old man with recurrent RET-positive lung adenocarcinoma who developed CA 17 months after starting selpercatinib. Reducing the selpercatinib dose and implementing a low long-chain triglyceride diet led to symptom relief, stable ascites, and maintained tumor response. This case highlights effective management of tyrosine kinase inhibitor (TKI)-induced CA without compromising cancer control.