ABSTRACT
<p><b>OBJECTIVE</b>To study the values of immunohistochemistry staining and cytological diagnosis by using cell block sections prepared with the effusion fluid cytology specimens.</p><p><b>METHODS</b>Ninety-nine effusion cytology specimens with the diagnoses of reactive mesothelial hyperplasia, atypical cells and metastatic carcinoma were enrolled into the study. The cytospin preparations/smears, cell block sections and immunohistochemical study were performed and correlated with the clinical findings and follow-up data.</p><p><b>RESULTS</b>Amongst the 99 cases studied, the percentage with positive diagnosis using cytospin preparations/smears was 68.7% (68/99). The percentages with negative and equivocal diagnoses were 16.2% (16/99) and 15.1% (15/99), respectively. As for cell block sections, the percentages were 71.7% (71/99), 16.2% (16/99) and 12.1% (12/99), respectively. On the other hands, the percentages became 76.8% (76/99), 20.2% (20/99) and 3.0% (3/99), respectively, when coupled with immunohistochemical findings. The overall percentages of positive, negative and equivocal diagnoses were 77.8% (77/99), 17.2% (17/99) and 5.0% (5/99), respectively, upon clinicopathologic correlation. The difference between cytospin preparations/smears and cell block sections was not statistically significant (P > 0.05). When coupled with immunohistochemical findings or clinicopathologic correlation, the difference in rates of equivocal diagnosis however carried statistical significance (P < 0.05). The false-negative rate of immunohistochemical study applied on cell block sections was 1.0% (1/99).</p><p><b>CONCLUSIONS</b>Immunohistochemistry, when applied on cell block sections, is useful in delineation of the primary origins of the tumor cells in effusion fluid cytology specimens. Combination of morphologic examination, immunohistochemical findings and clinicopathologic correlation can further improve the rate of positive diagnosis.</p>