What is S100?

S100 is a specialized protein that is made by many different types of normal, healthy cells including cells in the skin, salivary glands, fat, cartilage, and nerves. Tumours that start from these types of tissue may also make S100. Once the S100 protein is made, it is held in both the nucleus and cytoplasm of the cell. The nucleus is the part of the cell that holds most of the cell’s genetic material (DNA) while the cytoplasm is the body of the cell that surrounds the nucleus.

What tests do pathologists perform to look for S100?

Pathologists use a test called immunohistochemistry to ‘see’ S100 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 S100. 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.

Normal types of tissues and cells that produce S100

  • Skin – Melanocytes and Langerhans cells
  • Salivary glands – Myoepithelial cells
  • Fat – Adipocytes
  • Cartilage – Chondrocytes
  • Nerves – Schwann cells
  • Brain and spinal cord – Glial cells
  • Lymph nodes – Dendritic cells

Non-cancerous tumours that produce S100

Cancers that produce S100

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