Biotechnology Healthcare - September/October 2008 - (Page 25)

A false HER2-positive comes with a price: 52 weeks of chemotherapy and trastuzumab exceeds $50,000 plus the expense of relieving the side effects. that the results of its home brew test are “concordant” with an FDAapproved test kit. “The strategy for doing that is, without doubt, to save money, because it’s far cheaper to make your own home brew than to buy the packaged FDA-approved kits,” says Jeffrey S. Ross, MD, Cyrus Strong Merrill professor and chair of the Department of Pathology and Laboratory Medicine at Albany Medical Center in Albany, N.Y. He is one of the developers of the FISH test and has conducted central-lab work for several neoadjuvant trastuzumab trials. Ross, who specializes in breast and genitourinary pathology, enumerates three of the many ways even an FDA-approved HER2 test kit in a central lab can generate an incorrect result: • A second assay on a new slice of formalin-fixed, paraffin-embedded tissue that comes from a different part of the tumor may generate a different result. Although infrequent, tumors can be HER2-positive in some places and HER2negative in others. • Sometimes, the whole chromosome on which the HER2 gene is located (along with thousands of other genes) is amplified in the tumor tissue. It’s called chromosome 17 polysomy, and it can be misinterpreted as HER2 gene amplification. • A technical error in an IHC assay (for instance, the dispenser that releases a drop of staining reagent on the slide fails to open) can be detected only by including a tissue specimen known to score 3+ on the same slide as the tissue being tested.1 If such a control specimen is not used, an absence of staining can be misinterpreted as a negative test result. FISH assays have a built-in control to prevent false negatives. Experienced pathologists know how to avoid these pitfalls, but most HER2 assays are not done by experienced pathologists. The ASCO/ CAP Guideline Recommendations are designed to eliminate these and other sources of variation in HER2 testing by codifying validation of “home brew” tests and standardizing operating procedures, and by complying with new testing criteria to be monitored through the use of stringent laboratory accreditation standards, proficiency testing, and competency assessment. The guideline recommendations are being implemented and enforced by CAP. One thing the guideline recommendations don’t do is give the nod to either IHC or FISH. In fact, ASCO/CAP go out of their way to avoid any preference. In the results section of the abstract, the authors write: “When carefully validated 1 testing is performed, available data do not clearly demonstrate the superiority of either immunohistochemistry (IHC) or in situ hybridization (ISH) as a predictor of benefit from anti-HER2 therapy.” Such even-handedness, though, is not supported by the evidence, according to one dissenting author of the guideline recommendations. A brief look at the difference between IHC and FISH may help to clarify this difference of opinion. IHC VERSUS FISH In an IHC assay, a slice of tumor tissue is stained, along with a 3+ control specimen in a corner of the slide, and then the tumor sample in question is examined with a bright field microscope. The amount of observed staining correlates with the quantity of HER2 protein. Subjective decisions in scoring a tissue specimen are opportunities for variability in an IHC HER2 assay. Even flawless technique and interpretation can still generate a FISH result in what pathologists call the “indeterminate” range of 1.8 to 2.2, which means another slice of the tumor tissue has to be tested using a FISH assay. “With immunohistochemistry, the results can vary based on how long the tissue is fixed and what antibody you use for the staining. Many, many variables can influence the result,” says Paik, who nevertheless agrees with the majority of the ASCO/CAP expert panel that FISH is not superior to IHC. “You also have to judge the scoring based on how strong the staining is, and that can be quite subjective. You could have two pathologists looking A tumor tissue is scored 3+ when it has a “full basket weave” appearance (a series of dark brown touching circles around the cells) in at least 30 percent of the sample. If the basket weave pattern has “holes” in it — for example, if the circles don’t extend 360 degrees around the cells or if the pattern comprises less than 30 percent of the total specimen — it’s scored a 2+. A weak staining pattern drops the score to 1+, and no visible staining is a 0. SEPTEMBER/OCTOBER 2008 · BIOTECHNOLOGY HEALTHCARE 25

Table of Contents Feed for the Digital Edition of Biotechnology Healthcare - September/October 2008

Biotechnology Healthcare - September/October 2008 Openers Editorial/David B. Nash, MD, MBA Contents At a Glance: Multiple Sclerosis Drug Track Personalized Medicine Healthcare Reform’s Effects on Biologic Access Breast Cancer Status Testing: A Crapshoot With Deadly Odds Trends, Issues, and Perspectives In the Management of MS So High-Tech, Yet So Simple The Evolution of Ascertaining the Value Proposition Specialty Pharmacy Employer to Employer Health Plan Confidential Trends

Biotechnology Healthcare - September/October 2008

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