Synaptophysin is a protein made by specialized neuroendocrine cells. These types of cells are found in the brain and in endocrine organs such as the thyroid gland, adrenal gland, and pancreas. Small groups of neuroendocrine cells can also be found in non-endocrine organs throughout the body such as the stomach, small bowel, colon, skin, bladder, and lungs. Cells use synaptophysin to make a specialized piece of cellular machinery called a secretory granule. These secretory granules hold and release chemicals called transmitters and are used to send signals between cells. Synaptophysin is often found with another protein called chromogranin.
Pathologists use a test called immunohistochemistry to ‘see’ synaptophysin inside cells. The synaptophysin protein is normally found in a part of the cell called the cytoplasm or cell body.
Pathologists often perform immunohistochemistry for synaptophysin to help identify neuroendocrine cells in a tissue sample. This test can be performed to look for normal neuroendocrine cells or to see if a tumour is made up of abnormal neuroendocrine cells. The term neuroendocrine tumour is used to describe a tumour that is made up entirely of neuroendocrine cells. The term neuroendocrine carcinoma is used to describe an aggressive type of cancer made up entirely of neuroendocrine cells.
Positive for synaptophysin means that immunohistochemistry was performed and synaptophysin was seen inside the cells of interest. Reactive is another term that pathologists use to describe cells that are producing synaptophysin.
Negative for synaptophysin means that immunohistochemistry was performed and synaptophysin protein was not seen inside the cells of interest. Non-reactive is another term that pathologists use to describe cells that are not producing synaptophysin.