Methods: A prospective cohort of patients with PE from different etiologies will be recruited stating on 11.21.2013 and prospectively ending on 11.21.2023. Data will be collected within 4 hours of admission including history, chest X-ray, and blood and pleural fluid (PF) cell counts and basic biochemistry. Pleural fluid and serum will be biobanked for future analyses. Patients will sign informed consent forms. Diagnosis will be confirmed using standard microbiology, cytology, histology, and imaging techniques. Patients undiagnosed within a month will be excluded. Variables will be entered into binary regression and receiver-operator analyses using malignancy as the target to develop the MAPED score, a clinical score that predicts malignancy at admission. MAPED will be retrospectively validated in separate published cohorts from the first therapeutic interventions in malignant effusion (TIME) 1-3 trials from Oxford UK. Data will be censored and analyzed three times, at 40-month intervals since study initiation.