This biomarker shows high sensitivity but moderate specificity for mesothelial lineages and, in detail, calretinin is 80–100% sensitive for PEM but it is also expressed in other neoplasms, such as lung squamous cell carcinomas (expression reported in approximately 35–40% of cases), lung adenocarcinomas (expression reported in approximately 0–10% of cases), breast carcinomas (expression reported in approximately 15% of cases and up to 38% of triple-negative breast carcinomas), and renal cell carcinomas (expression reported in approximately 0–10% of cases). This evidence concerns the gene CALB2 and triple-negative breast carcinoma.