HER2 is a cell membrane-spanning protein with functional extracellular and intracellular domains. The extracellular portion of HER2 interacts with HER2 molecules as well as other oncogenic proteins whereupon a signal is transduced to the intracellular portion, instructing cells to grow and divide. In cancer cells, extra copies of the HER2 gene increase the number of HER2 molecules on the cell surface, increasing the HER2 interactions and promoting aggressive tumor cell growth. Although HER2 is only one of several proteins capable of stimulating tumor cell growth, it is one of the few where targeted therapeutics have been developed that specifically interfere with extracellular protein interactions and intracellular cell growth signaling. Some of these drugs (Herceptin, for example) block interaction of the extracellular domain of HER2, thereby preventing HER2-driven cell division. Others, such as Tykerb, enter the cell and directly inhibit the tyrosine kinase signaling pathway that triggers cell growth.
The external portion of HER2 found in serum is referred to as the extracellular domain (ECD). Enzymes in the blood cleave the ECD at the cell surface, and small amounts of ECD are present in all sera. When HER2 is overproduced, higher amounts of ECD are present. This is the rationale for our serum HER2 test. Many HER2 tumors result in serum levels above the normal range. A 20% rise from one test to the next is considered evidence of HER2 tumor growth, while effective drug therapy results in a 20% decrease in as little as three weeks.
HERTEST is a quantitative sHER2/neu ELISA test. The ELISA is a common laboratory procedure used to measure many proteins (analytes) in the blood serum. Our test is performed in our CLA certified national reference laboratory that employs a sHER2/neu ELISA test kit cleared by the FDA.