The highest rate of TTF-1 positivity was found in various subtypes of thyroidal cancers (19.0–100%), adenocarcinomas of the lung (94.3%), neuroendocrine tumors (NET) of the lung (66.7%), small cell neuroendocrine carcinomas (NEC) of various organs of origin (71.4–80.0%), various categories of mesenchymal tumors (16.7–41.9%), and in thymomas (39.1%). This evidence concerns the gene TTF1 and mesenchymal cell neoplasm.