Routine immunohistochemical markers (CDX2, SATB2, Islet 1 and TTF-1) may help identify one of the more common primary sites, but if a pituitary tumor was previously diagnosed, additional immunohistochemistry (including pituitary hormones and/or pituitary transcription factors) may be helpful to evaluate for the rare possibility of pituitary carcinoma. The gene discussed is TTF1; the disease is pituitary adenocarcinoma.