p40 is a protein made by several types of normal, healthy cells, including squamous cells, basal cells, and myoepithelial cells. These are specialized cells found in different parts of the body. For example, squamous cells line the skin and many internal surfaces, basal cells are found in particular layers of the skin and airways, and myoepithelial cells help support glands like the salivary and sweat glands.
Tumours that start from these types of cells often also make p40, which can help pathologists identify the type of tumour under the microscope.
Once the p40 protein is made, it stays in the cell’s nucleus. The nucleus is the control center of the cell and contains most of the cell’s DNA, which carries the genetic instructions the cell needs to function.
Pathologists use immunohistochemistry (IHC) to look for p40 in cells from a tissue sample. This test uses special dyes that bind to the p40 protein, making it visible under a microscope. IHC is a valuable tool because it helps pathologists confirm whether the cells in a tumour are related to squamous cells, basal cells, or myoepithelial cells, which normally make p40.
Testing for p40 is especially helpful when pathologists are trying to determine the type of tumour they are looking at. Tumours that produce p40 are often made up of squamous cells, basal cells, or myoepithelial cells. This information helps pathologists:
Pathologists can make a more accurate diagnosis by combining the results of p40 testing with other information, such as the tumour’s location, appearance under the microscope, and other immunohistochemical markers.