Rapid Progression of Lung Cancer Following Emergency Caesarean Section Led to Postpartum Acute Respiratory Failure

: Our case patient was a 38-year-old pregnant Japanese woman who underwent emergency Caesarean section because of massive vaginal bleeding due to a low-lying placenta. Immediately after delivery, she presented with rapidly progressive dyspnea. Contrast-enhanced computed tomography revealed bilateral pleural effusion, lung nodules, multiple liver tumors, and multiple osteolytic lesions. Accordingly, epidermal growth factor receptor-mutant advanced lung adenocarcinoma was diagnosed. This report highlights the occurrence of rapid progression of lung cancer following delivery that led to postpartum acute respiratory failure, rather than due to pulmonary thromboembolism associated with the existing deep venous thrombosis of the inferior vena cava.