Pleural Effusion Secondary to Tumor Regression

2 patients with metastatic cancer (Ewing’s sarcoma and breast cancer) developed pleural effusions while undergoing systemic therapy for pulmonary metastases. Thoracenteses failed to reveal malignant cells and in both instances the characteristics of the fluids were those of transudates. The effusions developed in association with dissolution of pulmonary lesions and presumably represent a reactive process to tumor regression