TTF1 and Merkel cell skin cancer: TTF-1 IHC has also been suggested to assist in the distinction of pulmonary from non-pulmonary neuroendocrine neoplasms [42], the distinction of Merkel cell carcinoma of the skin from cutaneous metastases of pulmonary small cell carcinoma [43], and as a marker for thyroidal carcinomas of all types including medullary carcinoma [44].