TTF1 and malignant colon neoplasm: In fact, retrospective immunostaining of the original colon tumor block (performed after the metastatic focus was found to be TTF-1 positive) showed patchy TTF-1 nuclear staining in the primary tumor as well (focally 1–5% of cells, Fig. 8), confirming that the primary colon cancer itself aberrantly expressed TTF-111.