January 25, 2007

In this Issue...

Taking Aim at Accuracy:
New HER2 Testing Guidelines Aim to Decrease False-Positive Results
by Julie McDowell

Even though determining HER2 gene status in women diagnosed with breast cancer is now an important element of guiding patient treatment, an estimated 10–20% of results from current HER2 tests are believed to be inaccurate. Recently, in a joint effort, the College of American Pathologists (CAP) and the American Society of Clinical Oncology (ASCO) released guidelines to improve the accuracy of HER2 testing. As a result of these guidelines, CAP will now require accredited labs conducting HER2 testing to participate in proficiency testing for the marker. This issue of Strategies will analyze these guidelines and highlight the key aspects of the recommendations that pertain to the clinical laboratory.

Since the FDA approved the cancer fighting drug trastuzumab, or Herceptin, in 1998, concerns about inaccuracy have plagued HER2 testing, whether the test is performed using immunohistochemistry (IHC) or through amplification of the gene by fluorescence in situ hybridization (FISH). However, clinicians have become reliant on the results of this test as the sole determinant in making treatment decisions, according to Antonio Wolff, MD, FACP, Associate Professor of Oncology at the Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins in Baltimore, Md.

“When Herceptin was approved by the FDA, there was the realization that a large percentage of test results could be inaccurate and that a large number of patients with false positive tests were being exposed to a potentially toxic and costly placebo,” he explained, adding that the drug carries a small risk of serious cardiac toxicity. Even though these concerns had been well known, it wasn’t until data from recent clinical trials first presented at ASCO’s Annual Meeting in 2005 that the effectiveness of this drug in reducing the risk of recurrence and mortality, whether used alone or in conjunction with other therapies, was clarified.

These concerns prompted the pathology and oncology communities to develop recommendations—the ASCO/CAP Guideline Recommendations for Human Epidermal Growth Factor Receptor 2 Testing in Breast Cancer—which were jointly published in the January 2007 issues of the Archives of Pathology & Laboratory Medicine (Vol. 131, pp. 18-43) and the Journal of Clinical Oncology (Vol. 25:118-145, 2007).

“This drug is changing the natural history of women with early stage HER2-positive breast cancer, and therefore it became critical to make sure we were identifying who would be or should not be a candidate for Herceptin treatment,” said Wolff, who is co-lead author of the guidelines. “In addition, HER2 status can serve also as a prognostic factor and in some cases, may also influence the optimal choice of various kinds of endocrine therapies and chemotherapies. For various reasons, it was critical that we addressed these accuracy issues.” While there has been controversy over which method—IHC or FISH—is better, the authors concluded that there is currently not evidence to justify using one assay over the other.

New PT and Fixation Recommendations

For the clinical laboratory, an important element of the guidelines will be the testing algorithms for both IHC and FISH (see graphic below).

Also of interest to clinical labs will be the new HER2 proficiency testing (PT) requirements. While CAP-accredited laboratories are expected to enroll in HER2 PT this year, it will not officially become part of the accreditation process until 2008, explained Patrick Fitzgibbons, MD, a pathologist at St. Jude Medical Center (Fullerton, Calif.), and the Chair of CAP’s Immunohistochemistry Committee. In addition to successful participation in PT, labs will have to prove they’ve annually validated their assays, demonstrating 95% concordance with another validated HER2 test for both positive and negative assay values with at least 25 cases. This means, for example, that labs doing HER2 by IHC will have to test at least 25 cases with both FISH and IHC, and achieve a minimum of 95% concordance for positive results, and 95% concordance for negative results.

Another issue that will impact labs involves fixation of the sample, which is believed to be a major source of preanalytic variation in testing. If staining is done when the tissue is either over or under fixed, this can have a significant impact on the result, explained Fitzgibbons. “For many labs, this may be the element in the guidelines that requires the most change,” he added. “The guidelines specify that you should not do HER2 testing on specimens that have been fixed for less than six hours or more than 48 hours. It doesn’t sound like a major problem and it shouldn’t be for cases that are done Monday through Thursday, but if a patient has a breast biopsy done Thursday night or Friday, ordinarily that tissue would be sitting in formalin from that point until Sunday night when the tissue processor starts its cycle, so it would be longer than 48 hours.” A 3-day or holiday weekend presents a bigger problem. If a patient has a biopsy done on the Friday of a holiday weekend, her tissues will be fixed for 72 hours before processing.

Labs will have to find a solution to this problem, said Fitzgibbons. One alternative is to have histology come in on the weekends and embed the tissues in paraffin. “Another alternative would be to convince surgeons to do these kinds of procedures on Monday through Thursday, although that may be difficult,” said Fitzgibbons. Labs can also request surgeons to notify them if a biopsy is performed on Friday or during the weekend, so an alternative processing schedule can be planned.

Another issue is the type of fixative used by the laboratory. Most HER2 assays have been standardized using neutral buffered formalin, and while alternatives do exist, the guidelines indicated that formalin is the preferred fixative. Labs choosing to use an alternative fixative must validate their methods against formalin. “You have to validate that your stain is achieving the same results as those formalin fixed assays have also done,” explained Fitzgibbons.

As both clinicians and laboratorians digest and implement these new PT and fixation recommendations, it’s clear that accuracy will remain a priority because HER2 testing is such an integral part of cancer care. “Clinicians and patients in routine practice are making critical therapeutic decisions based on this one assay, so we need to be in a situation where the clinician and patient can trust the results of the assay, regardless of where the results are coming from,” said Wolff. “Hopefully as these guidelines are implemented and as procedures are put in to place over the next year, such as assay validation and proficiency testing, we will be able to trust the results of the assays and not be worried about the possibility of inaccurate results, and then go on to make the best decision possible for our patients.”

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Julie McDowell is the Editor of Strategies. She can be reached by email.

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