MSLN and neoplasm: In ovarian cancer, MSLN has been found to be overexpressed in 55–97% of (high-grade) serous ovarian tumors.9,10 High-grade ovarian cancer is characterized by a complex tumor microenvironment, with buildup of malignant ascites and widespread (micro-) metastatic lesions across the peritoneal surfaces and omentum.11,12 Despite overexpression of MSLN, its expression is not homogenous within primary tumors and multifocal metastatic lesions of MSLN+ classified samples.9,10