Breast Cancer HER2 Test For Herceptin Candidates Approved By FDA

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Main Category: Breast Cancer
Also Included In: Medical Devices / Diagnostics;  Regulatory Affairs / Drug Approvals
Article Date: 09 Jul 2008 - 3:00 PDT

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The US Food and Drug Administration (FDA) announced on Tuesday that it had approved a new test that measures the strength of HER2 gene amplification in breast cancer patients so that decisions can be made about whether they should be given the cancer drug Herceptin (trastuzumab).

HER2 genes control the growth, division and repair of breast cells, and when overexpressed this leads to too many HER2 proteins sending too many signals to grow cells which results in unregulated growth and cancer. The gene is overexpressed in around 18 to 30 per cent of breast cancers.

The new genetic test is made by Invitrogen of Carlsbad, California, and is called the SPOT-Light HER2 CISH kit. The test is based on a technology called chromogenic in situ hybridization (CISH) which uses a DNA probe to look at the HER2 gene in a small sample of stained tumor tissue.

According to information on the manufacturer's website the essence of CISH is it uses labelled nucleic acid probes to bind to specific sections of complementary nucleic acid in the sample so that probe results can then be seen in the context of the surrounding tissue structure. This is an advantage because the pathologist can see the tissue structure and the gene defects at the same time.

The new kit uses a standard bright-field microscope as opposed to a specialized and more expensive fluorescent microscope, so it can be used outside of specialized reference labs. Also, the test results are quantifiable which overcomes the subjectivity inherent in more traditional tests based on immunohistochemistry (IHC) interpretation, said the manufacturer in a prepared statement. And, unlike existing tests, the new test allows labs to store the tissue samples for future reference.

According to the manufacturer's instruction manual, the results must be interpreted "within the context of the patient's clinical history by a qualified pathologist".

Vice president and general manager of Invitrogen's Cellular Analysis Business, August Sick, said:

"The current protocol for assessing HER2 gene status is for labs to initially screen tissue samples with immunohistochemistry to gauge whether there is an overabundance of the HER2 protein, as an indirect measure of gene amplification."

"In the case of an inconclusive test, the samples are typically sent to an outside lab for confirmation. Because the SPOT-Light(R) HER2 CISH Kit doesn't need specialized equipment, any histology lab can now assess amplification of the HER2 gene while simultaneously examining tissue morphology," added Sick.

Dr Jeffrey Ross, Cyrus Strong Merrill Professor and Chair of the Department of Pathology and Laboratory Medicine at Albany Medical College, New York, welcomed the announcement, saying that:

"Given the emerging potential use of trastuzumab [Herceptin] in the adjuvant setting, the need to accurately determine the front-line HER2 status in breast cancer has never been more critical."

Ross said the new test had proved to be as good as the fluorescent in situ hybridization (FISH)-based assay for pinpointing HER2 gene over-expression, now considered the standard for confirming a patient's eligibility for treatment with Herceptin.

"Testing for HER2 status in breast cancer by CISH takes advantage of the best attributes of FISH using familiar, fast and low cost IHC detection techniques. This is a true marriage between the two procedures," he added.

Dr Daniel Schultz, director of the FDA's Center for Devices and Radiological Health said:

"When used with other clinical information and laboratory tests, this test can provide health care professionals with additional insight on treatment decisions for patients with breast cancer."

The FDA approved the new test on the strength of a study that used tumor samples from breast cancer patients in the US and Finland.

Herceptin (trastuzumab) is manufactured by Genentech, of San Francisco, California. It is only effective in patients whose tumors show HER2 gene amplification and/or protein over-expression.

Sources: FDA, Invitrogen.

Written by: Catharine Paddock, PhD


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