Peritoneal effusion: an uncommon adverse effect of selective RET inhibitors

Chylous effusion is a rare side-effect observed during treatment with multikinase inhibitors (MKIs) or selective RET tyrosine kinase inhibitors.1 Pleura (12/22, 54%), peritoneum (5/22, 23%), or both (5/22, 23%) are the common sites for chylous effusion. Selpercatinib (15/217, 7%) and MKIs (7/7371, <1%) are the most frequent causes. No confirmed effusion cases were observed with pralsetinib, but two patients with RET-rearranged non-small-cell lung cancer on pralsetinib had chylous ascites in a recent case series.2 The time to event varied from 0.5 to 50 months for MKIs and 1.6 to 19.5 months for selpercatinib. Following initial drainage, the RET inhibitor dose, primarily selpercatinib (13 cases), was reduced in 52% (14/22) of patients with no need for dose discontinuation.1