Another possible origin of a TTF-1 positive follicular tumor metastatis is struma ovarii, which is a very remote possibility, as are other follicular neoplasms, entering differential diagnosis such as serous and small cell carcinoma of the ovary, intrahepatic cholangiocarcinoma or breast tumors with follicular morphology [5,9]. Here, TTF1 is linked to ovarian small cell carcinoma.