TTF1 and lung adenocarcinoma: For adenocarcinomas with a similar histomorphology to that of primary breast tumors, a differential diagnosis should be made by immunohistochemical examination.[20,21] CK7 analysis is useful in determining the origin of metastatic lesions and strongly indicated that all samples from our patient were of either breast or lung origin.[22] Although thyroid TTF-1 is expressed in 68% to 76% of lung adenocarcinomas, positivity in breast adenocarcinoma has never been reported.[23]