Malignancies in Pleural, Peritoneal, and Pericardial Effusions

CONTEXT.—: The incidence and types of malignancies in effusion cytology are largely limited to studies performed in the 1970s through the 1990s. OBJECTIVE.—: To examine how the incidence of different types of malignancies in effusions has changed with time. DESIGN.—: A computerized search for fluid cytology from 2000 through 2016 (database included age, gender, cytologic diagnosis, and type of malignancy) was performed, and all cases were reviewed. RESULTS.—: Of 30 085 effusion specimens, 3285 (11%) were positive for malignancy (2175 pleural, 955 peritoneal, and 155 pericardial). Of those, 1023 (31%) had known primary sites (648 pleural, 267 peritoneal, and 108 pericardial). Malignancy was more common in females than males in both pleural (15% versus 9%) and peritoneal (14% versus 5%) effusions (P < .001). The most common metastatic tumors in pleural fluid were lung for males and breast for females; in peritoneal fluid, hematolymphoid for males and Müllerian tumors for females; in pericardial fluid, lung for both genders. Among invasive mammary carcinomas, lobular carcinoma tended to metastasize to peritoneal fluid, whereas ductal carcinoma tended to metastasize to pleural fluid (P < .001). Plasma cell neoplasms metastasized to pleural and pericardial but not peritoneal fluid (P = .002). CONCLUSIONS.—: Although pulmonary and Müllerian tumors continue to be the most common origin of metastasis in pleural and peritoneal fluid for males and females, respectively, the frequencies for other malignancies have changed. Familiarity with the more common sites of metastasis in effusion cytology is important, especially in patients with unknown primary, as this will be valuable in judicious triaging of specimens for ancillary studies.