Manganese superoxide dismutase as a diagnostic marker for malignant pleural mesothelioma

Although several immunohistochemical markers are available, differential diagnosis between mesothelioma and metastatic adenocarcinoma of the pleura is difficult. We have found that the immunoreactivity of manganese superoxide dismutase (MnSOD), an important antioxidant enzyme, is high in mesothelioma compared to healthy pleural mesothelium. The aim of the present study was to investigate whether MnSOD can be used in the differential diagnosis of malignant mesothelioma and metastatic adenocarcinoma of the pleura. MnSOD expression was assessed by using immunohistochemistry in biopsies of malignant mesothelioma (n = 35) and metastatic adenocarcinoma of the pleura (n = 21). MnSOD immunoreactivity was assessed semiquantitatively with and without microwave pretreatment. Fifteen of the 35 malignant mesotheliomas showed moderate or strong MnSOD expression without and 23 with microwave pretreatment, the corresponding figures for metastatic adenocarcinoma of the pleura being 1 and 2 out of 21 (P = 0.002 and P < 0.001, respectively by Fisher's exact test). Only mesothelioma biopsies showed strong MnSOD reactivity, and it was never negative in mesothelioma, whereas one-third of the adenocarcinomas showed no MnSOD reactivity. In conclusion, MnSOD immunoreactivity can, combined with other markers, aid the differential diagnosis between malignant mesothelioma and metastatic adenocarcinoma of the pleura.