First Report of RET Fusion-Positive Lung Adenocarcinoma With Miliary Intrapulmonary Metastases Responsive to Selpercatinib: A Case Report

Lung cancer presenting with miliary lung metastases on chest computed tomography is associated with poor prognosis. Recent studies indicate that non-small cell lung cancer harboring driver gene mutations, including rearranged during transfection (RET) fusions, can manifest with miliary lung metastases. However, the efficacy of molecularly targeted therapies in RET fusion-positive non-small cell lung cancer with miliary dissemination remains unknown. Here, we report a case of a 45-year-old man with a right lower lobe lung nodule, bilateral miliary intrapulmonary metastases, extensive lymphadenopathy, and metastases to the left adrenal gland, liver, and multiple bones. Transbronchial needle aspiration confirmed lung adenocarcinoma, with RET fusion detected via gene panel testing. Treatment with selpercatinib resulted in a sustained partial response for over one year, providing the first clinical evidence supporting this targeted therapy in RET fusion-positive lung adenocarcinoma with miliary metastases.