Validation of commonly used immunostains on cell-transferred cytologic specimens

BACKGROUND. Immunocytochemical staining (ICC) is often limited by the lack of cell blocks that contain diagnostic cells or by the unavailability of smear materials. The cell-transfer technique, in which original smear material is divided into several pieces and then transferred to multiple slides, can facilitate multiple ICC on limited materials. However the reliability of the staining results has not been systematically evaluated. METHODS. The authors validated 21 commonly used antibodies (cytokeratin [CK] 7, CK 20, TTF-1, panCK, vimentin, HMB-45, Mart-1, leukocyte common antigen, chromogranin, synaptophysin, estrogen receptor, progesterone receptor, prostate-specific antigen, prostatic acid phosphatase, calretinin, CK5/6, WT-1, BerEP4, MOC-31, p63, and thyroglobulin) on the cell-transferred materials of various tumor samples (n = 20) and reactive effusion samples (n = 2). The staining results were compared with the previously available ICC results (performed either on cell block sections or on smears) of the same specimens. RESULTS. One hundred pieces of transferred materials were immunostained, of which 5 (5%) were lost during the staining procedure. Of the remaining 95 pieces, 92 (97%) showed staining results that agreed with those of the previous ICC, whereas 3 (3%) showed results that disagreed. The original ICC in the latter three specimens was performed on cell block sections and showed focally positive synaptophysin staining in a sample with a neuroendocrine tumor, focally positive CK5/6 staining in a pleural effusion sample with mesothelioma, and positive TTF-1 staining in a lymph node sample with metastatic lung carcinoma. Their corresponding ICC of cell-transferred materials showed negative results. An increase in background staining was observed in 1 of the 95 tissue pieces, but no false-positive results were observed. CONCLUSIONS. In general, ICC can be reliably performed on cell-transferred tissue specimens for markers tested. However, caution should be taken when interpreting ICC results in tissue specimens with limited cellularity and heavy background staining.