The tissue from a breast biopsy is preserved and examined by the pathologist. If the biopsy shows breast cancer, most often several tests are performed to further characterize the tumor. Proteins on the surface of the cancer cell or the DNA of the genes inside the cells can be measured in the preserved tumor tissue. The results of these tissue tests are important in considering future treatment. One set of tests looks for the protein HER2/neu. If there is an excess of HER2/neu the woman may be a candidate for treatment with HER2-targeted drugs, usually given in addition to the common chemotherapy drugs.
HER2 tumors tend to be more aggressive and more likely to spread, either before initial diagnosis, or sometime later. Also, the HER2 tissue test result may not be accurate. For example, the biopsy may have missed a HER2 portion of the tumor that is more prone to spread. Therefore, the HER2 status of tumors is an ongoing issue for every patient.
It helps to measure HER2/neu in the blood serum of women with metastatic breast cancer; the HER2/neu protein breaks off and circulates in the serum. Serum levels of the protein HER2/neu most often go up during the course of progression and drop with successful treatment. Some years ago, a Boston researcher developed a test to accurately measure the level of HER2/neu in the serum—serum HER2/neu is often shortened to sHER2/neu and sometimes sHER2. This test is called a quantitative sHER2/neu ELISA—we call it HERTEST. The test received 510(k) certification for use in metastatic breast cancer from the U.S. Food and Drug Administration in 2000. In 2002, the test received a government billing approval, known as a CPT Code.
We recommend a baseline serum level be determined once evidence of metastatic disease is documented We suggest repeated at intervals during the course of progressive, metastatic breast cancer.