TTF1 and colorectal carcinoma: Moreover, the specificity of IHC is not always useful for distinction: e.g. TTF1 CK7, CDX2 and CK20 do not have any distinctive capacity between primary intestinal carcinoma from the lung and a metastasis from a colorectal carcinoma, as the IHC pattern is the same: TTF1-, CK7-, CDX2+ and CK20+ [40].