GATA-3 is a specialized protein that is made by many different types of normal, healthy cells including cells in the skin, breast, salivary glands, kidney, bladder, and immune system. Tumours that start from these types of tissue may also make GATA-3. This protein may also be found in tumours that start in tissues that do not normally make GATA-3. Once the GATA-3 protein is made, it is found in the nucleus of the cell. The nucleus is the part of the cell that holds most of the cell’s genetic material (DNA).
Pathologists use a test called immunohistochemistry to ‘see’ GATA-3 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 GATA-3. Cells that make this protein will be called positive or reactive. Cells that do not make this protein will be called negative or non-reactive.