Application of the immunoperoxidase technique to cell block preparations from fine needle aspirates.

Immunocytochemistry on fine needle aspiration (FNA) material has been mainly performed on cytologic preparations; there have been few reports on the use of FNA cell blocks. This study compared the intensity scores of immunoperoxidase staining on FNA cell block preparations from 21 breast, 12 thyroid and 10 lymph node aspirates with the scores on the corresponding surgically excised specimens. FNA materials for cell blocks were fixed in formalin and embedded in agar. Ten commercially available antibodies forming three panels were studied using standard peroxidase-antiperoxidase and avidin-biotin complex techniques. In general, the staining results on the FNA cell block sections agreed with those on the surgical specimens; in addition, there were fewer aberrant positive staining results and much less background staining in the cell block sections. These phenomena were most striking with the cytokeratin antibodies. It is concluded that immunoperoxidase staining on FNA cell block preparations is reliable; the advantages of the use of cell block sections as opposed to smears are discussed.