CellBlockistry: Chemistry and art of cell-block making - A detailed review of various historical options with recent advances.

Cell-blocks are paraffin-embedded versions of cytology specimens comparable to the formalin-fixed paraffin-embedded (FFPE) tissue from surgical pathology specimens. They allow various elective ancillary studies on a variety of specimens with enhanced cytopathologic interpretation, including opportunity to perform molecular tests. However, different dictionaries and internet search engines primarily project "cellblock" and "cell block" definition in relation to prisons. Most of the top searches lead to information related to "prison cells" followed by a few cytopathology-related searches. Due to this in the current review, it is recommended that the word for cytopathology purposes should be hyphenated and spelled as "cell-block." Cell-blocks have been increasingly indicated on most cytology specimens. Its role is growing further with the ongoing addition of new immunohistochemistry (IHC) markers with technical advances including multicolor IHC and the SCIP (subtractive coordinate immunoreactivity pattern) approach. In addition, it is an important source of tissue for many ancillary studies even as archived material retrospectively at later stage of management if the cell-blocks are improved qualitatively and quantitatively. Because of this, the significance of cell-block is critical with the increasing number of molecular markers standardized predominantly on FFPE tissue. As compared to core biopsies, high-quality cell-blocks prepared with enhanced methodologies predominantly contain concentrated diagnostic tumor cells required for the molecular tests without significant stromal contamination. This review introduces the terminology of CellBlockistry as the science of studying chemistry and the art of achieving quantitatively and qualitatively improved cell-blocks from different types of specimens. The review addresses the cell-block making process as "cell-blocking" and discusses different historical limitations with emphasis on recent advances.