The American Society of Clinical Oncology (ASCO) and the College of American Pathologists (CAP) have issued a joint, updated guideline aimed at improving the accuracy and reporting of human epidermal growth factor receptor 2 (HER2) testing in patients with invasive breast cancer. The guideline update is based on a systematic review of medical research literature, providing oncologists and pathologists with detailed recommendations on testing for HER2 over-expression, interpreting the results, and recommending HER2-targeted therapies.
Approximately 15% of newly diagnosed breast cancers are HER2-positive: the tumors have extra copies of the HER2 gene and/or high levels of the HER2 protein, which controls breast cancer cell growth and spread. HER2-positive tumors usually grow faster than HER2-negative tumors. The purpose of HER2 testing is to identify patients who could benefit from effective HER2-targeted therapies, such as trastuzumab (Herceptin), lapatinib (Tykerb), pertuzumab (Perjeta), and T-DM1 (Kadcyla), as well as patients for whom such therapies would be ineffective.
The two FDA-approved methods now used in the United States to test for HER2 are immunohistochemistry (IHC) and in situ hybridization (ISH). IHC testing assesses how much HER2 protein is present on the surface of tumor cells, while ISH testing measures how many copies of the HER2 gene are present inside each cancer cell. The original guideline focused on IHC and fluorescence in situ hybridization (FISH); the updated guideline adds recommendations for a newer diagnostic technique, bright-field ISH. This technique also evaluates for amplification of the HER2 gene, and uses a regular light microscope rather than a fluorescent microscope. Read more information on the new guideline, including a link to a PDF of its publication in the Journal of Clinical Oncology.
