Cytopathology in focus: Serous fluid cytology and the international system

Last bastion in cytopathology standardization

Barbara A. Crothers, DO
Daniel F.I. Kurtycz, MD; Ashish Chandra, MD
Fernando Schmitt, MD, PhD

January 2019—Just when you thought you were done implementing a new terminology for cytology, another one pops up.

Is it possible there are sites that have not yet been standardized? Unbelievably, the most common nongynecologic cytology specimen, body fluids, remains a Wild West for terminology, and the International Academy of Cytology and American Society of Cytopathology are collaborating to improve consistency and understanding for serous fluid cytology reporting by developing The International System for Reporting Serous Fluid Cytology, or TISRSFC.

The intention is to produce an atlas with text similar to those published for existing cytopathology terminology: the Bethesda systems for reporting cervical cytology and thyroid cytopathology, the Milan System for Reporting Salivary Gland Cytopathology, the Papanicolaou Society of Cytopathology systems for reporting pancreaticobiliary cytology and respiratory cytology, the Paris System for Reporting Urinary Cytology, and the future Yokohama System for Reporting Breast Cytopathology.

To align with precedent cytology terminology systems, the proposed categories for the new system for serous fluid cytology will be non-diagnostic (ND), negative for malignancy (NFM), atypia of uncertain significance (AUS), suspicious for malignancy (SFM), and malignant (MAL). Additional special sections will address cytopreparatory techniques, quality assurance, and issues related to peritoneal washings and mesothelioma.

Creating standardized terminology for serous fluid cytology is not without its challenges. Serous effusions are often evaluated for metastases and there are many diagnostic possibilities for metastatic tumors, involving many different body sites. Fortunately, pathologists are equipped with special stains and immunocytochemistry and molecular tests that can specifically characterize most metastatic tumors, and this will be a particular focus of this effort. AUS and SFM can be considered preliminary categories that are reported as a last resort, when all possible subsequent studies cannot define the disease process. The proposed publication will provide the reader with an approach to metastases using ancillary studies and clinical information.

Another confusing area in serous fluid cytology is the presence of epithelial cell groups in peritoneal washings. In some cases, these are benign Müllerian-origin cells exfoliated by abrasive procedures or saline jet streams projected against the peritoneal surfaces. They may be spontaneously exfoliated from proliferative processes such as endometriosis and endosalpingiosis. Benign and malignant cells may be introduced by virtue of operative procedures that result in expulsion of cells from the endometrium into the peritoneal cavity. There is little data on the reporting of, and outcomes for, these findings, and this will be a task for the international system team to unravel.

Why, you may ask, is a new terminology system necessary? First, let us explore prior medical advances that have been made with implementation of standardized cytology terminology, using as an example The Bethesda System for Reporting Cervical Cytology (TBS). As the first standardized terminology adopted by the cytopathology community, TBS has remained a cornerstone and the model for subsequent terminology systems. It is widely accepted and, in some cases, is a requirement for medical publication in the United States. TBS has allowed for relatively reliable and consistent comparison of published study results—reliable in that the criteria for each category are outlined and consistent because it is the preferred terminology. Understandably, there are still uncontrolled subjective variables with the interpretation of cells that will never be standardized, but coming as close as possible to agreement in diagnosis is always a goal in medicine.