Bronchiolitis obliterans organizing pneumonia (BOOP) is generally idiopathic; however, this lesion may be caused by more than 35 medications and from breast radiotherapy. These drugs include the cancer chemotherapeutic agents, antibiotics, cardiovascular drugs and immunosuppressive agents noted in Table 24.1. 1,2 Unproductive cough is a common early symptom and shortness of breath occurs later. Fever is also often seen early. Eosinophila is unusual. The radiograph shows bilateral patchy infiltrates, and the chest CT shows ground-glass opacities, often peripheral and pleural-based (Fig. 24.1). Mid-lung computed tomography scan showing BOOP as a posterior ground-glass opacity and consolidation with an air bronchogram that is triangular, with the apex at the mediastinum and the base at the posterior pleura. https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9780429166983/3b1f5adf-73e6-436e-9011-9d2297f08321/content/fig24_1.tif"/>