Thames Valley Cytology Society

Immunocytochemistry in Cytopathology

Report by Parita Patel, Northwick Park Hospital

At Wexham Park Hospital on 29th October 2002, Mr Ian Phillips gave a very interesting presentation on the use of immunocytochemistry in cytopathology. Mr Phillips highlighted the technical and diagnostic issues of immunocytochemistry (ICC).

He began by defining immunocytochemistry as a "technique used for identifying cellular constituents by means of a specific antigen-antibody interaction, the site of antibody binding being identified either by direct labelling of the antibody, or by the use of a secondary method."

Immunocytochemistry has gradually developed into a major diagnostic tool in cytopathology being of assistance in the differential diagnosis of FNAs and serous fluids where diagnosis on morphological grounds only can be extremely difficult. The use of various antibodies can accurately identify cell types such as epithelial cells from mesothelial cells and also differentiate small single cell types.

There are a number of methods possible for the preparation of cytological specimens for immunostaining. Air dried cytospin preparations on poly-l-lysine slides followed by fixation has been found to be the most popular and suitable method. However, with cytospins it is necessary to check for the presence of cells before staining.

The limitations of cytologic material can be overcome by the use of cell blocks, frozen sections, or wax embedded material. The common fixatives used for cytologic preparations produce an often intolerably high background staining that mars interpretation. Methanol, ethanol, acetone and formal saline are found to be the best fixatives for immunocytochemistry.

A variety of sensitive immunostaining procedures and reagents are currently available and all can be applied to cytologic preparations with equally good results, given that careful attention is paid to technical detail, especially cell preparation techniques. Diagnostic pitfalls and limitations persist, so strict morphological criteria should still be applied when trying to interpret results.

The adoption of modifications for cytological samples and adherence to technical guidelines could reduce the impediments to the realization of the full potential of ICC in diagnostic cytopathology.

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Positive results for the above stains have a high specificity and sensitivity for adenocarcinoma over mesothelioma.

Negative results for all four stains can be interpreted as strongly favouring malignant mesothelioma.