Utility of cytology microarray constructed from effusion cell blocks for immunomarker validation

BACKGROUND: Tissue microarray allows rapid and efficient evaluation of gene expression at the protein level and of immunochemical markers. To our knowledge, there has been no report of constructing cytology microarray using effusion cell blocks and testing its utility in immunochemical marker validation. METHODS: A total of 23 malignant effusions (primary tumor of breast 5, GI tract 5, lung 5 and ovary 8) were used to construct a cytology microarray so that 3 cores of 0.6 mm in diameter were taken from the original cell blocks. Antibodies including AE1/AE3, EMA, and Ki-67 were applied to all cases, and CK7, CK20, TTF-1, WT-1, ER, and PR antibodies were used for selected cases. The cellularity, composition of cells, the staining pattern, and the intensity of each antibody were compared between corresponding cell block sections and CMA cores. RESULTS: The composition of tumor cells in the original block and the cores (including Sections 1 and 45) on cytology microarray were similar, ranging from 5% to 90%. Immunostains of AE1/AE3 and EMA were all positive and 100% concordant between the originals and cytology microarray. Similarly, CK7, CK20, ER, PR, TTF-1, and WT-1 stained both original blocks and cytology microarray with a high level of agreement with respect to percentage of positive cells, staining pattern (cytoplasm or nuclear), and intensity. Ki-67 stain showed slightly lower concordance (84%) with a few cases not in agreement because of low tumor burden in the original block coupled with low percentage of staining by antibody. CONCLUSIONS: Three 0.6 mm cores of cytology microarray are representative of the original cell block with cellularity and antibody staining pattern, intensity, and percentage. Therefore, CMA has a great potential in clinical research and practice as it allows rapid validation of immunocytochemical markers.