TTF1 and breast cancer: Currently, there are many relatively specific immunohistochemical markers or combinations used for the auxiliary diagnosis of breast cancer, including GATA3, mammaglobin, GCDFP-15, and ER, similar to how TTF-1 and NapsinA are used for diagnosing lung cancer, CDX2 for gastrointestinal-origin cancers, TG for thyroid cancer, Hepatocyte and Arg-1 for liver cancer, and PSA and AR for prostate cancer, etc. However, these so-called site-specific markers are not highly specific, and abnormal expression can occur in rare cases.