在转移性癌，原发癌鉴别诊断时，TTF-1的陷阱。
（研究证明多种肿瘤中都有TTF-1的表达）
Thyroid Transcription Factor-1 Expression in Breast Carcinomas
Am J Surg Pathol 2010;34:1881–1885
Abstract: Immunostaining for thyroid transcription factor-1
(TTF-1) is frequently used to help assess the site of origin of
metastatic carcinomas. TTF-1 expression is most frequently seen
in carcinomas of thyroid and lung origin. Furthermore, it has
been assumed that the expression of TTF-1 in a carcinoma excludes
the possibility of a breast origin. We have recently encountered
in our consultation practice 4 cases of invasive breast
carcinoma (confirmed by clinical findings and other immunophenotypic
features) that showed unequivocal tumor cell expression
of TTF-1. However, the frequency with which TTF-1
expression is observed in breast carcinomas is unknown. To
address this, we carried out immunostaining for TTF-1 on 546
primary breast carcinomas submitted for routine estrogen receptor,
progesterone receptor, and/or HER2 testing. Cases were
considered TTF-1 positive if they showed any nuclear staining
for this marker. TTF-1 expression was identified in 13 cases (2.4%).
Expression varied from focal and weak to diffuse and strong and
was seen in both invasive and in situ components. We conclude
that a small proportion of breast carcinomas show TTF-1
expression. Therefore, the presence of TTF-1 immunoreactivity
in a carcinoma cannot by itself be used to exclude the possibility
of a breast origin.