Trastuzumab is a monoclonal antibody, one of a group of drugs designed to attack specific cancer cells.
Trastuzumab – Trastuzumab Biologics
Trastuzumab’s targets are cancer cells that overexpress an oncogene called HER2 or HER2/neu, which occurs in high numbers in about 25 to 30 percent of breast cancers. According to the National Comprehensive Cancer Network (NCCN), breast cancers can be categorized as being HER2 positive or HER2 negative. HER2-positive breast cancer is faster growing and considered more aggressive. Studies indicate that the drug trastuzumab (Herceptin) is effective in treatment of HER2-positive early stage breast cancer and HER2-positive metastatic breast cancer. Trastuzumab is not effective in the treatment of HER2-negative breast cancers.
There are two methods of testing for HER2 tumor status in women with breast cancer: immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH). HER2 test results are interpreted as follows:
HER2 positive status is IHC 3+ or FISH positive
HER2 negative status is IHC 0, 1+ or FISH negative
A borderline IHC result of 2+ should be followed by performing a FISH test.
A borderline FISH result of an average HER2 gene/chromosome 17 ratio of 1.8 to 2.2 (or an average of greater than 4 to less than 6 HER2 gene copies/cell) should be followed by one of the following:
Counting additional cells in the tissue sample
Retesting with FISH
Performing an IHC test
Results from both tests are used in the clinical setting, and the results of the tests influence treatment choices for women with breast cancer. The pathology laboratory where the HER2 testing is done should be accredited to perform such testing. It should have quality control procedures in place to ensure that the test is done correctly, and a quality assurance plan to validate (i.e., determine the accuracy of) the HER2 test results.
