TTF-1 (stands for thyroid transcription factor –1) is a specialized protein that is produced by normal cells in the lung, thyroid gland, thymus, and brain. Tumors that start from one of these organs may also produce TTF-1. This protein is normally found in a part of the cell called the nucleus. The nucleus holds most of the cell’s genetic material (DNA) while the cytoplasm is the body of the cell that surrounds the nucleus. Another name for TTF-1 is NKX2.1.
Pathologists use a test called immunohistochemistry to ‘see’ TTF-1 protein inside cells. Pathologists will perform this test when they are trying to decide if the cells that they are looking at under the microscope are one of the cell types that normally make TTF-1, or to help identify a tumour that can produce TTF-1. In this test, cells that make this protein will appear brown and will be called positive or reactive. Cells that do not make this protein, on the other hand, will appear blue and will be called negative or non-reactive. In order for a cell to be called positive, the TTF-1 should be seen in the nucleus of the cell.