Specific biomarkers and IHC staining are essential in differentiating MPeM from adenocarcinoma or perıtoneal plasmacytoma.2 Positive staining of tumor-suppressor gene (WT1), calretinin, and D2-40 as IHC and negative staining with carcinoembryonic antigen (CEA), thyroid transcription factor 1 (TTF-1), and claudin-4 are necessary for MPeM confirmation.6–8 The protein associated with breast cancer-susceptibility gene 1 (BRCA1), another molecular marker also detected in IHC, is important in distinguishing malignant mesothelioma from reactive ones.9,10. The gene discussed is CEACAM5; the disease is breast cancer.