A Rare Presentation of Pneumonic-Type Adenocarcinoma Hidden behind Empyema

Pneumonic-type adenocarcinoma (P-ADC) can closely mimic pneumonia. We report a P-ADC initially diagnosed as pneumonia which developed into a pulmonary abscess and empyema. A 50-year-old Japanese male diagnosed with pneumonia, pulmonary abscess, and empyema was administered antibiotics and a chest tube for drainage, which improved his symptoms and blood test results. However, chest computed tomography showed an enlarged infiltrative shadow. The patient underwent bronchoscopy and was diagnosed with an adenocarcinoma. This case highlights the importance of considering P-ADC in differential diagnoses when a pneumonia-like shadow enlarges post-empyema treatment. Diagnostic and clinical tests, e.g., bronchoscopy, should be performed in such cases.