LAUSR

Malignant pleural mesothelioma is associated with asbestos exposure and poor outcomes. The usefulness of immunohistochemistry for diagnosis of sarcomatoid mesothelioma, especially the desmoplastic type, is limited and more effective markers are required. GATA3 has been suggested as a diagnostic marker for sarcomatoid mesothelioma. The potential usefulness of GATA3 for prognostication and its clinical and pathological correlations in different subtypes of mesothelioma have not been evaluated. We investigated the immunohistochemical labelling and associations for GATA3, BAP1 and Ki67 labelling in three major histological types of pleural malignant mesotheliomas. We examined149 clinically annotated malignant mesotheliomas and assessed associations of GATA3 expression with clinical variables and prognosis. In addition, we labelled 10 cases of fibrous pleuritis with GATA3, all of which were negative. GATA3 was positive in 75/149 (50%) mesotheliomas with the highest incidence of labelling seen in the sarcomatoid subtype (73%), compared to the biphasic (50%) and epithelioid (40%), mesotheliomas. A total of eight desmoplastic mesotheliomas showed labelling with GATA3. Patients with sarcomatoid histology showed poorer survival compared to the other subtypes. (p<0.001), but overall GATA3 labelling did not have a statistically significant association with survival (p=0.602). There was no association of GATA3 labelling and BAP1 status or Ki67 index. Conclusion: Our study includes the largest cohort of mesotheliomas that has been labelled for GATA3 to date. GATA3 is a useful marker for sarcomatoid mesothelioma, including the desmoplastic subtype. Discordance in GATA3 and BAP1 labelling of epithelioid and sarcomatoid components in the biphasic subtype is not uncommon.