Immunohistochemistry was pivotal in diagnosis, with tumour cells in both peritoneal and gallbladder tissues staining positively for D2–40, WT1, CK7, and CK5/6, and negatively for BerEP4, confirming metastatic epithelioid mesothelioma. This evidence concerns the gene KRT5 and malignant epithelioid mesothelioma.