Fluorescent in-situ hybridization (FISH) may be a more accurate test to determine whether a breast cancer patient is Her-2 positive, as recently reported at the 37
th Annual Meeting of the American Society of Clinical Oncology.
HER2-positive breast cancer refers to a specific type of breast cancer in which the cancer cells display an overabundance of small proteins on their outer surface called
human epidermal growth factor receptor 2 protein (HER2). HER2 proteins bind exclusively with other proteins called growth factors. The binding action between HER2 and growth factors facilitates cancer cells to replicate and grow in an uncontrolled manner.
Herceptin® is the first monoclonal antibody that has been approved by the FDA for the treatment of breast cancer. Monoclonal antibodies are proteins that can be made in the laboratory and are designed to recognize and bind to very specific sites on a cell. Herceptin® is a monoclonal antibody that binds to the HER2 protein. This binding action achieves anti-cancer benefits through two distinct processes. First, the binding of Herceptin® blocks growth factors by binding to HER2, thereby eliminating the stimulating effects on cancer cells. Second, the binding action of Herceptin® appears to stimulate the immune system to attack and kill the cancer cells to which Herceptin® is bound. A previous clinical has demonstrated that treatment with Herceptin® plus chemotherapy improves outcomes compared with chemotherapy alone in patients with HER2-positive advanced breast cancer.
The conventional laboratory test utilized to determine the HER2 status of a patient is called an immunohistocompatibility (IHC) test. IHC detects HER2 proteins through specialized staining of tumor cell membranes. These samples are then categorized according to the degree of HER2 overexpression (0 to 3+, the latter being the highest rating of HER2 overexpression). Recent research, however, indicates that the laboratory method referred to as FISH may more accurately detect the presence of HER2 overexpression in cancer cell samples. FISH methods directly test the DNA of a cancer cell to determine HER2 status at a genetic level.
Recently, researchers have been trying to determine which of these tests should be utilized as standard testing for HER2 status. One clinical study reported a 12% discrepancy between IHC and FISH test results. The majority of these discrepancies occurred in patients whose results were 2+ according to IHC. Another clinical study evaluating this issue revealed that out of 111 patients with advanced breast cancer who tested IHC-positive, only 82 tested FISH-positive. When Herceptin® was used as a single agent for treatment, the IHC-positive patients had a 26% response rate and the subgroup of FISH-positive patients had a 34% response rate. Time to disease progression was 3.5 months for IHC-positive patients and nearly 5 months for FISH-positive patients. One more clinical trial indicated that anti-cancer response rates for IHC-positive patients with advanced breast cancer receiving Herceptin® was 15%, compared with 19% for FISH-positive patients. Overall survival was 12.8 months for the IHC-positive patients and 14.2 months for FISH-positive patients.
Since response rates to Herceptin® may be utilized as an indicator of the true HER2 status, the results of these trials suggest that FISH testing more accurately determines HER2 status than the conventional IHC testing. It is imperative that patients with breast cancer get tested for HER2 status, as clinical studies have demonstrated improved survival when Herceptin® is added to chemotherapy versus chemotherapy alone in HER2-positive patients. In addition, patients may wish to speak with their physician about getting FISH testing versus IHC testing for the determination of HER2 status. (
Proceedings from the 37
thAnnual Meeting of the American Society of Clinical Oncology
, San Francisco, CA, May, 2001)
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