However, although it is not absolute, WT1 shows the highest specificity among common mesothelial biomarkers, showing lack of expression in lung adenocarcinomas [3,45,56] and renal cell carcinomas [3,45,63], virtually no expression in lung squamous cell carcinomas (only 0–2% of reported positive cases) [3,45,57], and a very low expression in breast carcinomas (5–8% of reported positive cases) [3,45,54]. This evidence concerns the gene WT1 and lung adenocarcinoma.