Histopathologic examination confirmed malignant mesothelioma of epithelioid type, supported by immunohistochemical reactivity for calretinin, cytokeratin 7 (CK7), cytokeratin 5/6 (CK5/6), pan-cytokeratin (PanCK), Wilms tumor 1 (WT1), and loss of BRCA1-associated protein-1 (BAP1). The gene discussed is KRT5; the disease is malignant mesothelioma.