First Report of <scp> <i>RET</i> </scp> 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 (<i>RET)</i> fusions, can manifest with miliary lung metastases. However, the efficacy of molecularly targeted therapies in <i>RET</i> 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 <i>RET</i> 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 <i>RET</i> fusion-positive lung adenocarcinoma with miliary metastases.