Use of HER2 Gene Test and Herceptin Needs Review

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Use of the HER2 gene test, which identifies certain aggressive breast cancers that respond to a specific drug, appears to be greatly underutilized, according to a new study published online in the journal Cancer. The drug, Herceptin, also is being given to some women who have never been tested for it, which may increase their risk of serious heart problems.

The HER2 gene test is used to identify breast cancers for which the drug Herceptin (trastuzumab) is useful. HER2 is a specialized protein (receptor) located on the surface of breast cells and breast cancer cells. This protein controls the growth, invasion, and spread of cancer to other parts of the body. All healthy breast cells have two copies of the HER2 gene, which controls production of the HER2 protein. About 20 percent of women with breast cancer have high levels of the HER2 gene and/or protein. These women are said to have HER2-positive tumors, which tend to be high risk and more invasive, and they also often respond differently to some types of treatment.

One of the anticancer drugs that specifically blocks HER2 is Herceptin , which has Food and Drug Administration approval to treat HER2-positive breast cancer. Two challenges presented by Herceptin are high cost and that it causes serious cardiac side effects in a small number of users, including an inability to pump blood effectively, irregular heartbeats, high blood pressure, heart failure, weakening of the heart muscle, and sudden death.

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Therefore it is critical to accurately determine which women with breast cancer have HER2-positive tumors, and to ensure that women who have HER2-positive tumors are offered the drug while those with HER2-negative tumors are not given the drug to avoid potential side effects.

Guidelines for HER2 gene testing have been developed jointly by the College of American Pathologists (CAP) and the American Society of Clinical Oncology (ASCO). Among the recommendations are that HER2 status should be identified for each patient who has invasive breast cancer. According to the new study in Cancer, however, two-thirds of women with invasive breast cancer are not tested for the presence of HER2 abnormalities. The study also found that about 20 percent of HER2 tests performed by local laboratories provided inaccurate results when compared with results from larger laboratories that did tests on the same tissues.

The findings of the Cancer study highlight the need for clinicians to ensure that women who are diagnosed with invasive breast cancer undergo HER2 gene testing. The study results also indicate that a significant number of women with breast cancer who are taking Herceptin likely should not have been prescribed the drug and are therefore at risk for life-threatening heart problems.

SOURCES:
Bloomberg, September 14, 2009
College of American Pathologists

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