Primary lung adenocarcinoma mimicking recurrent pneumonia in a young adult.

A man in his 20s with a history of tobacco use presented with recurrent shortness of breath. He was hospitalised three times within the past 4 months for similar symptoms despite completing several courses of antibiotic therapy. In this presentation, he was afebrile with rhonchi and decreased breath sounds over the right lung. Chest CT demonstrated large consolidations in the right middle and lower lobes, worsened compared with 4 months prior. Infectious workup including bronchoscopy with bronchoalveolar lavage did not identify a causative organism. Testing for immune disease was negative. Transbronchial biopsy ultimately identified well-differentiated stage 3b lung adenocarcinoma with a KRAS G12C mutation. The patient was referred to oncology for outpatient follow-up and has since initiated chemotherapy. This case highlights diagnostic biases encountered in young patients and the utility of bronchoscopic biopsy for definitive diagnosis in presumed community-acquired pneumonia when the clinical outcome is not improving as expected.