Pitfalls in Immunocytochemical Study Using Fine Needle Aspiration Samples
Immunostaining of histopathological specimen is carried out using formalin-fixed paraffin-embedded tissues with or without antigen retrieval. Meanwhile, immunostaining of fine needle aspiration (FNA) smear is usually carried out using 95% alcohol-fixed specimens. The immunostaining results obtained with histopathological specimens and those with cytological specimens may be discrepant or even contradictory due to the differences in fixatives, fixation methods, and/or antigen activation treatment. An automated immunostaining instrument in our hospital is used for the special care in fixation of cytological smears. For FNA smear, alcohol fixation is used, which is followed by further fixation with phosphate-buffered formalin solution and an antigen activation treatment. Useful immunostaining markers in diagnosis of thyroid tumors are shown in Table 57.1.