S100

S100 is a protein normally found inside many different types of cells in the human body. It plays a role in various cellular processes, such as cell growth and communication. Pathologists can use special tests to detect this protein in tissues, which can help them diagnose certain types of tumours and other medical conditions.

What types of cells normally express S100?

S100 is most commonly found in cells of the nervous system, such as nerve cells (called neurons) and supporting cells (called glial cells and Schwann cells). It is also found in immune system cells (like dendritic cells), skin cells (called melanocytes), fat cells, cartilage, and salivary glands. These tissues all normally express this protein, and its presence can be an important indicator in diagnosing certain conditions.

What types of tumors express S100?

S100 is expressed in a wide variety of tumours. These tumours often arise from tissues that normally express this protein, such as the nervous system, melanocytes, salivary glands, fat, or cartilage. The presence of S100 in these tumours can help pathologists determine the type of tumor and guide treatment decisions.

Examples of benign (non-cancerous) tumours that express S100:

• Schwannoma: A type of tumour that develops from Schwann cells, which surround and protect nerve fibers.
• Neurofibroma: A benign tumour that grows from the nerves and may be part of a genetic condition called neurofibromatosis.
• Melanocytic nevi (moles): These are common, harmless growths of melanocytes in the skin.
• Pleomorphic adenoma: A benign tumour of the salivary glands that can express S100.
• Chondroma: A benign tumour made up of cartilage tissue that can express S100.
• Myoepithelioma: A benign tumour that arises from myoepithelial cells, commonly found in salivary glands, and often expresses S100.
• Granular cell tumour: A rare, usually benign tumour that can develop in various parts of the body and typically expresses S100.

Examples of malignant (cancerous) tumours that express S100:

• Melanoma: A type of skin cancer that arises from melanocytes. S100 is often used to help diagnose melanoma.
• Malignant peripheral nerve sheath tumor (MPNST): This rare cancer develops from the cells surrounding nerves and is often seen in people with neurofibromatosis.
• Clear cell sarcoma: A rare type of cancer that usually develops in soft tissues, like tendons or muscles, and is often associated with melanocytic features.
• Liposarcoma: A cancer arising from fat cells that can sometimes express S100.
• Chondrosarcoma: A cancer that arises from cartilage cells and can express S100.
• Myoepithelial carcinoma: A malignant tumor arising from myoepithelial cells, often found in salivary glands and sometimes the skin, which can express S100.
• Synovial sarcoma: A rare cancer that typically develops near joints and can also express S100.

How do pathologists test for S100?

Pathologists use immunohistochemistry (IHC) to look for S100 in tissue samples. In this test, a small piece of tissue is treated with special antibodies that bind to the S100 protein. If the tissue contains this protein, the antibodies cause the cells to change color, which the pathologist can see under a microscope. This helps the pathologist determine if certain types of cells or tumours are present.

When do pathologists perform this test?

Pathologists perform this test when they need to confirm the presence of certain types of cells or tumours, particularly in cases where the diagnosis is unclear. For example, if a tumour is suspected to be melanoma or another type of tumour that normally expresses S100, this test can help confirm the diagnosis. It is also used to distinguish between different types of tumours that may look similar under a microscope.

About this article

Doctors wrote this article to help you read and understand your pathology report. Contact us if you have questions about this article or your pathology report. For a complete introduction to your pathology report, read this article.

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