An improved method for paraffin-embedded cytological preparations: application to the detection of circulating tumour cells.

Introduction: Conventional tissue biopsy is a key examination in cancer diagnosis. However, liquid biopsy is an alternative and less invasive solution that allows the detection of circulating tumour cells (CTCs). CTCs have emerged as a potential screening, diagnostic, and prognostic tool in cancer management. There are many technologies available for the detection and characterization of these cells, but most are either expensive or complicated to apply routinely. Cytological cell blocks (cytoblocks) may be a more practical and cost-effective method to enrich and characterize CTCs and even perform molecular studies. These cytoblocks allow the processing, analysis, and storage of cell suspensions and fluid aspiration samples containing CTCs. Material and methods: Here we detail a manual protocol based on isolation by density gradient centrifugation, formalin fixing, and paraffin embedding as well as morphological identification for cytological analysis and phenotyping by immunocytochemistry. This method is the result of technical adjustments of previously established protocols. Results: We succeeded in modifying a protocol for the construction of cytoblocks and applied it to study CTCs in lung and colorectal cancers, respectively. Conclusion: This less expensive protocol offers a possibility for use in routine diagnosis and can be applied in other fields of research, such as hematology for hematological malignancies and immunology.