CD117

CD117, also known as c-kit, is a protein that acts as a receptor on the surface of specific cells in the body. It is involved in cell growth, survival, and development, particularly in cells that form part of the blood, skin, and digestive system. This protein plays a critical role in normal cell function, especially in mast cells (a type of immune cell), and is also associated with the development of some benign and malignant tumours.

What types of cells and tissues normally express CD117?

This protein is normally found on the surface of various cell types, including mast cells, certain types of blood cells, and cells in the gastrointestinal tract. It is particularly abundant in mast cells, which play a role in the body’s immune response. In the gastrointestinal tract, it is present in the interstitial cells of Cajal, which help coordinate the movement of food through the digestive system.

How do pathologists test for CD117?

Pathologists use a test called immunohistochemistry (IHC) to detect this protein in tissue samples. Immunohistochemistry uses special proteins called antibodies that bind specifically to the target protein if it is present in the cells. When the antibodies attach to CD117, they produce a colour change that can be seen under a microscope. The pathologist examines the tissue to determine if the protein is present and notes the pattern and intensity of staining. The results are reported as “positive” (present) or “negative” (not present). This information can help pathologists identify specific types of tumours and guide further testing or treatment.

What types of benign (noncancerous) tumours express CD117?

Certain benign tumours can express this protein. An example is angiomyolipoma, a noncancerous tumour that often arises in the kidneys and is made up of blood vessels, muscle, and fat cells. Expression can also be seen in conditions like mast cell diseases, which involve the overgrowth of mast cells in the skin or other organs. These diseases are often also positive for other markers like tryptase, CD43, and CD68. Nasopharyngeal angiofibroma, a rare, benign tumour found in the nasopharynx (the area behind the nose), can also express this protein.

What types of malignant (cancerous) tumours express CD117?

A wide range of malignant tumours can express CD117, including:

• Acute myeloid leukemia (AML) – Commonly expressed in the cancerous cells of AML, a type of blood cancer that starts in the bone marrow.
• Gastrointestinal stromal tumour (GIST) – The expression of CD117 is a hallmark of GIST, a tumour originating from the interstitial Cajal cells in the digestive tract.
• Adenoid cystic carcinoma – This type of cancer often shows strong staining, which helps in its diagnosis.
• Angiosarcoma – Seen in about half of angiosarcomas, cancers originating from the cells lining blood vessels.
• Epithelioid sarcoma – A soft tissue tumour that can show expression, assisting pathologists in identifying the cancer.
• Ewing sarcoma – A cancer that often affects bones or the soft tissue around bones.
• Hodgkin lymphoma – Some Reed-Sternberg cells, the characteristic cells in Hodgkin lymphoma, may show positivity.
• Leiomyosarcoma – This cancer arises from smooth muscle cells, and the tumour cells can sometimes express CD117.
• Melanoma – A type of skin cancer, though not all cases will show this marker.
• Osteosarcoma – A cancer that starts in the bones and can sometimes show expression.
• Rhabdomyosarcoma – A cancer of muscle tissue, where some cases may express the protein.
• Seminomas/dysgerminomas – Germ cell tumours found in the testes or ovaries.
• Small cell carcinoma of the lung – An aggressive type of lung cancer that can be positive or CD117.
• Synovial sarcoma – Approximately 10% of cases show expression, usually within the cytoplasm of the cells.
• Thymic carcinoma – These cancers, which arise from the thymus gland, can show expression.
• Solid pseudopapillary tumour – About 50% of these rare pancreatic tumours are positive for this marker.

In some conditions, like intra-abdominal fibromatosis and mesenteric fibromatosis, expression depends on the specific antibody used during testing and can be variable.