ERG

ERG is a protein made by certain types of cells throughout the body. It belongs to a group of proteins called transcription factors, which control how cells turn specific genes on or off. By regulating genes, ERG plays a key role in developing and maintaining healthy blood vessels and can influence the growth of certain tumors. Normally, ERG is found inside the nucleus, the part of the cell that holds genetic material (DNA).

What types of normal cells and tissues express ERG?

ERG is normally produced by endothelial cells, specialized cells that line the inside of blood vessels. These cells form the inner lining of veins, arteries, and capillaries, helping control blood flow throughout your body. Because endothelial cells produce ERG, tissues rich in blood vessels, such as the lungs, heart, and kidneys, usually have high amounts of this protein. ERG can also be found in normal cells of the prostate gland.

How do pathologists test for ERG?

Pathologists perform a special test called immunohistochemistry (IHC) to check for ERG in tissue samples. This test uses antibodies designed specifically to attach to the ERG protein. When ERG is present in a cell, these antibodies bind to it and produce a visible color change. Pathologists examine the tissue under a microscope, looking specifically at the nucleus, since ERG normally appears there. The test results are reported as “positive” if ERG is seen or “negative” if ERG is not detected.

What types of benign (noncancerous) tumors express ERG?

Some benign (noncancerous) tumors that involve blood vessels produce ERG. An example is hemangioma, a common type of benign tumor made up of blood vessels. Since ERG is normally found in the lining cells of blood vessels, these types of tumors often show a positive test for ERG.

What types of malignant (cancerous) tumors express ERG?

Malignant (cancerous) tumors that start from blood vessel cells or contain lots of blood vessels frequently express ERG. Examples include angiosarcoma, Kaposi sarcoma, and epithelioid hemangioendothelioma. These cancers originate from cells that normally produce ERG, which is why this protein is present.

ERG can also be expressed by certain cancers that do not originate from blood vessels. For instance, prostate cancer (prostatic adenocarcinoma) sometimes produces ERG due to a genetic alteration known as a gene fusion. In this situation, the ERG gene becomes abnormally fused to another gene, leading prostate cancer cells to produce excessive amounts of ERG protein. Pathologists test for ERG to help identify prostate cancer and understand the specific genetic changes involved.

Additionally, ERG can be expressed by other cancers, including some Ewing sarcomas and certain types of acute myeloid leukemia (AML) or myeloid sarcoma. Identifying ERG in these cancers can help pathologists confirm the diagnosis and classify the specific type of tumor more accurately.