Mesothelial markers such as calretinin, D2-40, cytokeratin 5/6 (CK5/6), and Wilms tumour 1 (WT1) are typically positive, while epithelial markers such as carcinoembryonic antigen (CEA), Ber-EP4, MOC-31, and paired box gene 8 (PAX8) are negative, helping to distinguish MPM from peritoneal carcinoma or metastatic disease [3,10-12,14]. The gene discussed is CEACAM5; the disease is peritoneal carcinoma.