Utility of PAX 8 mouse monoclonal antibody in the diagnosis of thyroid, thymic, pleural and lung tumours: a comparison with polyclonal PAX 8 antibody

AIMS: The purpose of this study was to compare the immunohistochemical staining profiles of PAX8-polyclonal, PAX8-monoclonal, PAX5-monoclonal and PAX6-monoclonal antibodies in several histological types of primary thoracic and thyroid tumours. In addition, we analysed PAX8 mRNA expression by using in-situ hybridization. METHODS AND RESULTS: We compared polyclonal PAX8 and monoclonal PAX8, PAX5 and PAX6 antibodies in 962 samples (687 lung carcinomas, 40 malignant pleural mesotheliomas, 138 thymic tumours and 97 thyroid tumours) using the tissue microarray technique. Among thyroid tumours, the monoclonal and polyclonal PAX8 antibodies showed a high positive rate (98.0%). Of 167 polyclonal PAX8 antibody-positive tumours, except for thyroid tumours, 54 cases tested positive for PAX5 and/or PAX6 (31 lung carcinomas and 23 thymic tumours). No PAX8 mRNA expression was detected using RNAscope (in-situ hybridization technique) other than in thyroid tumours. A portion of polyclonal PAX8 antibody-positive tumours showed cross-reactivity for PAX5 or PAX6 protein. CONCLUSIONS: Monoclonal PAX8 antibody showed high specificity to thyroid tumours and was superior to the polyclonal antibody.