Quality Assurance in Immunocytochemistry: A Review and Practical Considerations

Abstract

Cytological samples play a critical role in diagnosing advanced stage tumors and those in difficult anatomical sites such as the pancreatobiliary tract, lung, thyroid, suprarenal, pelvis, or the salivary gland. They are often the only available material to realize accurate diagnosis and to perform ancillary studies, such as immunocytochemistry or molecular biomarkers. While the use of immunohistochemistry is well established and standardized on formalin-fixed-paraffin-embedded histological tissue (FFPE), in cytological samples it presents unique challenges due to the diverse ways to obtain and process this type of samples, which is not standardized between laboratories, but differs from one to another. Moreover, there is also diversity in the types of cytological samples potentially suitable for immunocytochemistry (ICC). This review explores the current landscape of ICC practices in European and North-American laboratories, highlighting variability in methods and the need for standardization to ensure reliable results and reproducibility of ICC on cytological specimens.