In a study by Naso et al., where tissue microarrays were used, positive HEG1 membrane IHC staining was observed in 94% of epithelioid mesotheliomas and negative membranous HEG1 IHC staining in all 167 (100%) NSCLC (73 pulmonary adenocarcinomas, 60 pulmonary SCCs, 21 pulmonary sarcomatoid carcinomas and 13 pulmonary large cell carcinomas) with the exception of one case of focal weak membrane staining in lung adenocarcinoma (scored as negative). The gene discussed is HEG1; the disease is malignant epithelioid mesothelioma.