RET-positive neuroendocrine lung cancer in pregnancy with placental metastases.

Lung cancer during pregnancy is rare, and placental metastases are exceptionally uncommon. Neuroendocrine lung tumours with RET point mutations have scarcely been reported in this setting.An early 40s G6P1031 woman at 33 weeks' gestation presented with dyspnea and flank pain. Imaging revealed a right lower lobe lung mass with hepatic metastases. Liver biopsy confirmed lung adenocarcinoma with neuroendocrine features and next-generation sequencing identified a RET p.M918T mutation. Following multidisciplinary discussion, labor was induced at 35 weeks with uncomplicated delivery of a healthy infant. Placental pathology demonstrated metastatic carcinoma consistent with pulmonary origin. The patient was treated with selpercatinib, resulting in radiographic response and clearance of circulating RET-mutant DNA. She remains progression-free 10 months into therapy and the infant continues normal development. This is the first reported case of RET p.M918T-mutated neuroendocrine lung cancer with placental metastases diagnosed during pregnancy, highlighting the importance of molecular profiling and multidisciplinary care.