Mesenchymal-epithelial transition factor exon 14 skipping mutation-positive granulocyte colony-stimulating factor-producing lung adenocarcinoma mimicking lung abscess: A case report.

Granulocyte colony-stimulating factor (G-CSF)-producing lung tumours are rare, with their imaging features and effective treatments remaining elusive. Similarly, mesenchymal-epithelial transition (MET) exon 14 skipping mutations are also uncommon. Herein, we report a case of G-CSF-producing lung adenocarcinoma positive for a MET exon 14 skipping mutation, mimicking lung abscess. A 61-year-old man presented with cough and high fever. Contrast-enhanced chest computed tomography revealed a mass with a cavity and internal fluid accumulation. The patient initially underwent diagnostic treatment for a lung abscess but was ultimately diagnosed with lung adenocarcinoma positive for a MET exon 14 skipping mutation. Following tepotinib therapy, the primary lesion shrank, and serum G-CSF levels decreased, leading to a diagnosis of G-CSF-producing lung cancer. G-CSF-producing lung tumours can present imaging findings that mimic lung abscesses. Tepotinib therapy may be effective for patients with MET exon 14 skipping mutation, including those with G-CSF-producing lung cancer.