Most episodes of pneumonia in patients with lung cancer are due to bacteria. This is particularly the case when risk factors of neutropenia, endobronchial lesions, underlying COPD and aspiration are present. Although opportunistic infections are not common, fungal infections should be considered if the patient has received a high dose of corticosteroids. Viral infections with herpes simplex, cytomegalovirus or respiratory syncytial virus may also rarely result in pneumonia in patients who have received highdose corticosteroids or very intensive chemotherapy.