Lung cancer may develop subsequently or coincidently with pulmonary alveolar proteinosis.

Pulmonary alveolar proteinosis (PAP) is a rare disease characterized by an accumulation of periodic acid-Schiff (PAS) positive lipoproteinaceous material in the alveolar space. It is usually idiopathic, and secondary to hematologic malignancy or some atypical infection. To date, there are only five published case reports of PAP occurring in association with solid organ cancer. We herein report two cases of PAP associated with lung cancer: one, a case of idiopathic PAP with subsequent development of lung cancer, and the other, a case of coexisting lung cancer and PAP. In conclusion, PAP can occur prior to or coincidently with lung cancer.