IMMUNOHISTOCHEMICAL PHENOTYPE OF MALIGNANT MESOTHELIOMA - PREDICTIVE VALUE OF CA125 AND HBME-1 EXPRESSION

Histological diagnosis of malignant mesothelioma and differentiation f rom adenocarcinoma is often difficult. Definitive pathological confirm ation of malignant mesothelioma requires demonstration of an appropria te immunohistochemical phenotype. Selection of an optimum panel of imm unohistochemical antibodies for the reliable identification of maligna nt mesothelioma is hindered by the absence of a specific immunohistoch emical label for mesothelioma cells. Recently, we have found that the ovarian carcinoma cell antibody CA125 labels malignant mesothelioma ce lls, and the antibody HBME-1 has been developed as a sensitive mesothe lial cell marker. We have compared the immunohistochemical staining pa tterns achieved with CA125 and HBME-1 to those obtained using a panel of eight further antibodies in 17 malignant mesotheliomas and 14 prima ry and secondary adenocarcinomas within lung and pleura. CA125 labelle d malignant mesothelioma cells in 15 of 17 cases (88%), and adenocarci noma cells in seven of 14 cases (50%). HBME-1 labelled mesothelioma ce lls in all 17 cases (100%) but also labelled adenocarcinoma cells in 1 0 of 14 cases (71%), BerEP4 positively labelled one the malignant meso thelioma but was negative in the remaining 16 cases and positively lab elled nine of 14 adenocarcinomas (64%). Monoclonal anti-CEA, AUA-1, CA 19.9 and LeuM1 labelled no malignant mesotheliomas and were positive i n 10 (71%), nine (64%), eight (57%) and six (43%) of 14 cases of adeno carcinoma, respectively. Diastase-PAS staining detected neutral mucin in none of the malignant mesotheliomas but in 10 (71%) of the 14 adeno carcinomas. We conclude that CA125 and HBME-1 do not label mesothelial cells with sufficient specificity to be useful for differentiating ma lignant mesothelioma from adenocarcinoma, although negative staining w ith HBME-1 makes a diagnosis of malignant mesothelioma unlikely. As th ere remains an absence of a specific positive mesothelial cell marker this distinction is still most reliably made using a panel of antibodi es including at least two of the following: anti-CEA, AUA-1, BerEP4, L euM1 and CA19.9, in combination with histochemical assessment of neutr al mucin production.