As a result of the availability and clinical efficacy
of trastuzumab (Herceptin), clinicians are now faced with a dilemma regarding
the accurate identification of patients with HER2 overexpression. In the October
2002 issue of ONCOLOGY, Monica Fornier and colleagues critically reviewed the
methodologies currently available for HER2 testing in their article, "HER2
Testing and Correlation With Efficacy of Trastuzumab Therapy."
The most widely used technique for detection of HER2 overexpression at the
protein level is immunohistochemistry (IHC). However, the problems with this
technique are, as correctly stated by the authors, that multiple primary
antibodieseach of which binds to different epitopes and has differing
sensitivities and specificitiesare currently in clinical use. Moreover,
different cutoff values are used to distinguish overexpressing form non-overexpressing
tumors. Detection of HER2/neu alteration is therefore not well standardized,
and although IHC detection methods are widely commercially available, some of
these assays may be suboptimal for this purpose.
Other IHC Limitations
Another concern is that the degree of IHC staining intensity for HER2 is
subjective and qualitative. As a consequence, it may be difficult to know
whether a sample scored as HER2-positive in one laboratory will be confirmed as
HER2-positive by another laboratory. Furthermore, formalin fixation of tumor
samples and storage in paraffin can result in epitope degradation so that
sensitivity is lost over time in archival clinical material.[3-5]
To overcome this problem, some assays use a technique called antigen
retrieval, which consists of boiling the tumor sample using heat or microwave
radiation, in order to rehabilitate epitopes that have been lost during tissue
processing and storage. Many believe that the loss of antigenicity in
paraffin-embedded specimens can be corrected by application of heat-induced
antigen retrieval to the paraffin-embedded tissue sections. However, this
approach has not been validated, before introduction of these reagents and
methods, by systematic evaluation of clinical breast cancer specimens with known
Detection Rate Variability
As summarized in the review by Fornier et al, reported detection rates for
IHC differ among clinical laboratories. This discrepancy has generated
considerable confusion among clinicians, pathologists, and patients regarding
the appropriate methods for HER2 testing. To address this issue, we recently
used each of the four US Food and Drug Administration (FDA)-approved assays for
detecting HER2 alterations, to determine which is the most accurate. We tested
these assays on breast cancer specimens in which we had previously determined
amplification and overexpression levels using solid matrix blotting techniques
as a "gold standard."
1. Fornier M, Risio M, Van Poznak C, et al: HER2 testing and
correlation with efficacy of trastuzumab therapy. Oncology 16:1340-1352, 2002.
2. Press MF, Hung G, Godolphin W, et al: Sensitivity of HER-2/neu antibodies
in archival tissue samples: Potential source of error in immunohistochemical
studies of oncogene expression. Cancer Res 54:2771-2777, 1994.
3. Slamon DJ, Clark GM, Wong SG, et al: Human breast cancer: Correlation of
relapse and survival with amplification of the HER-2/neu oncogene. Science
4. Pauletti G, Dandekar S, Rong H, et al: Assessment of methods for
tissue-based detection of the HER-2/neu alteration in human breast cancer: A
direct comparison of fluorescence in situ hybridization and immunohistochemistry.
J Clin Oncol 18:3651-3664, 2000.
5. Press MF, Slamon DJ, Flom KJ, et al: Evaluation of HER-2/neu gene
amplification and overexpression: comparison of frequently used assay methods in
a molecularly characterized cohort of breast cancer specimens. J Clin Oncol
6. Paik S, Bryant J, Tan-Chiu E, et al: Real-world performance of HER2
testingNational Surgical Adjuvant Breast and Bowel Project experience.
J Natl Cancer Inst 94:852-854, 2002.
7. Roche PC, Suman VJ, Jenkins RB, et al: Concordance between local and
central laboratory HER2 testing in the breast intergroup trial N9831. J Natl
Cancer Inst 94:855-857, 2002.
8. Vogel CL, Cobleigh MA, Tripathy D, et al: Efficacy and safety of
trastuzumab as a single agent in first-line treatment of HER2-overexpressing
metastatic breast cancer. J Clin Oncol 20:719-726, 2002.
9. Slamon DJ, Leyland-Jones B, Shak S, et al: Use of chemotherapy plus a
monoclonal antibody against HER2 for metastatic breast cancer that overexpresses
HER2. N Engl J Med 344:783-792, 2001.
10. Mass RD, Sanders C, Charlene K, et al: The concordance between the
clinical trails assay (CTA) and fluoescence in situ hybridization (FISH) in the
pivitol trials (abstract 291). Proc Am Soc Clin Oncol 19:75a, 2000.