Malignant-Primary (MAL-P) (Mesothelioma)

The diagnosis of malignant mesothelioma by cytology has been accepted in the last decade and guidelines for the diagnosis were previously published. This chapter focuses on the diagnosis and reporting of malignant mesothelioma by cytology and represents the consensus view of the authors and contributors who make the diagnosis of definitive malignant mesothelioma by effusion cytology on a regular basis. This chapter elaborates on the general approach to mesothelial effusions, key morphologic criteria of malignancy, appropriate utilization of immunohistochemistry, and the role of molecular and soluble biomarkers. A practical guideline is provided for the suggested diagnosis based on the constellation of findings. Fluids with atypical mesothelial cells can be cytologically diagnosed as malignant, suspicious, or atypical based on the cytologic findings and/or ancillary tests. The explanatory notes that follow provide detailed discussions of the differential diagnosis, diagnostic pitfalls, and useful ancillary studies to achieve an accurate diagnosis.