Autoimmune Pulmonary Alveolar Proteinosis with Suspected Exacerbation after Osimertinib Administration for Lung Cancer

A 46-year-old woman with lung cancer who received chemotherapy was admitted to our hospital for lower-lobe bilateral ground-glass opacity (GGO). GGO developed after the lung cancer diagnosis, deteriorated after the initiation of osimertinib, and incompletely decreased after interrupting osimertinib; therefore, flexible bronchoscopy was performed. Transbronchial lung biopsy histology and anti-granulocyte/macrophage colony-stimulating factor autoantibody positivity revealed autoimmune pulmonary alveolar proteinosis (aPAP) that did not require treatment. This rare case of aPAP comorbid with lung cancer suggested that using PAP findings to differentiate from drug-induced lung injury or lymphangitis is difficult and that osimertinib was suspected to exacerbate aPAP.