Subsequent investigations, including immunohistochemical and ultrastructural studies, proposed a unified origin, showing co-expression of thyroid markers (such as TTF-1 and thyroglobulin) and neuroendocrine markers (synaptophysin, chromogranin-A) in the carcinoid areas or transitional zones [2,3,4,5,6,7]. This evidence concerns the gene TTF1 and carcinoid tumor.