Since we observed higher expression of WT1 in immature mesothelial cells and lower expression in mature cells, and the reciprocal CALB2 expression pattern, the malignancy of mesothelioma is potentially related to the self-renewal capacity or immaturity of mesothelial cells regardless of its maturation or the defects of its maturation. The gene discussed is CALB2; the disease is mesothelioma.