Posted October 1, 2010
Erin Van Winkle Grimm, MD
One out of eight women will develop breast cancer, and nearly everyone has had a family member or friend who has combated this disease. A new drug in the treatment of breast cancer is trastuzumab, known under the brand name of Herceptin®. Trastuzumab therapy targets the transmembrane tyrosine kinase receptor known as human epidermal growth factor receptor-2, or HER2, which is encoded by the HER2 gene (also known as ERBB2 and CERB-B2) found on chromosome 17. Although there is physiologic expression of HER2 in non-neoplastic breast epithelium, this gene is highly amplified in 10-25% of breast carcinomas.1-4 The degree of HER2 amplification is both prognostic (untreated HER2-amplified cancers have a worse prognosis) and predictive (survival for HER2-amplified carcinomas improves on regimens that include trastuzumab).5
Patients with HER2-amplified breast carcinomas who receive trastuzumab have improved clinical outcome; however, the drawbacks include side effects such as cardiotoxicity and high expense. Therefore, distinguishing which patients will benefit from this drug is essential for optimum patient care. Laboratories use two central methodologies to determine HER2 status in the US: immunohistochemistry (IHC) and fluorescence in-situ hybridization (FISH). Both methods require interpretation of the test by a pathologist. Both methods were used in initial clinical trials for trastuzumab. IHC detects tissue antigens (in this case, the HER2 transmembrane protein) by using a labeled antibody. The HercepTest™ is a FDA-approved IHC method for assessing HER2 status where the intensity of staining observed is related to the number of receptors present on the cell membrane. Staining is titrated so that cells without HER2 amplification (normal epithelium or non-amplified neoplastic epithelium) have no or minimal staining, while neoplastic cells with amplified HER2 levels have strong, circumferential membrane staining. Studies show that non-amplified cells with no staining have less than half of the receptors compared with those with HER2 gene amplification.6 A category of intermediate HER2 overexpression exists, and these cases are referred to a second methodology, usually FISH.
FISH is a method that uses fluorescent probes that bind directly to a DNA sequence. The number of signals generated is directly related to the number of HER2 gene copies. Different FISH methods are FDA approved. Some methods assess HER2 amplification solely by determining the number of HER2 signals in a cell, while others require an amplified ratio of HER2 copies when compared to another chromosome 17 locus.
Immunohistochemistry is a common technique used daily by nearly all pathology laboratories in many applications (HER2 is one application). FISH is performed by fewer laboratories and often isn’t performed daily. FISH is more time intensive and more expensive. For these reasons, assessing HER2 by IHC is preferred by most laboratories. Since HER2 overexpression is directly related to gene amplification, one would expect the correlation between these two methods to be nearly 100%. However, there are reports of HER2 concordances below 80%.7
Attempts to explain and decrease discordances have been made. The scoring system initially introduced with the HercepTest has been modified to increase specificity by requiring a higher degree of staining to render a positive result. The American Society of Clinical Oncology (ASCO) and the College of American Pathologists (CAP) teamed up to publish guideline recommendations for HER2 testing, which attempt to standardize pre-analytical and analytical variables to improve overall concordance in both IHC and FISH methods.8 The guidelines require proof of internal quality assurance, adequate validation of the assay, and ongoing proficiency testing. These guidelines require concordance of 95% with another validated HER2 test. Accepted comparisons include FISH, an outside laboratory’s IHC, or other accepted but less common HER2 testing methologies. However, even with these improvements, some authors press for conversion of HER2 testing entirely to FISH with elimination of IHC testing.9 Other laboratories achieve >95% concordance between IHC and FISH, and therefore they believe IHC with reflex to FISH when necessary is a valid and cost-effective testing strategy.10,11
In summary, accurate HER2 testing is essential for quality patient care. However, no gold standard exists for HER2 testing, and pathology as a discipline is still debating the optimal testing strategy. Immunohistochemisty is the most widely used testing methodology with equivocal results reflexed for FISH testing. The ASCO/CAP HER2 guidelines published in 2007 attempt to standardize testing, and therefore, help patients receive accurate information regarding optimal treatment regimens for their breast carcinoma.
- 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. 1987; 235:177–182.
- Yaziji H, Goldstein LC, Barry TS, et al. Her-2 testing in breast cancer using parallel tissue-based methods. JAMA. 2004;291:1972-1977.
- Lal P, Salazar PA, Hudis CA et al. Her-2 testing in breast cancer using immunohistochemical analysis and fluorescence in situ hybridization: a single institution experience of 2279 cases and a comparison of dual-color and single-color scoring. Am J Clin Path. 2004; 121:631-636.
- Owens MA, Horten BC, Da Silva MM. Her2 amplification ratios by fluorescence in situ hybridization and correlation with immunohistochemistry in a cohort of 6556 breast cancer tissues Clin Breast Cancer. 2004;5:63-69.
- Ross JS, Slodkowska EA, Symmans WF, et al. The HER-2 receptor and breast cancer: Ten years of Targeted Anti-Her-2 Therapy and Personalized Medicine. The Oncologist. 2009;14:320-368.
- Konecny G, Pauletti G, Pegram M, et al: Quantitative association between HER-2/neu and steroid hormone receptors in hormone receptor positive primary breast cancer. J Natl Cancer In.. 95:142-153, 2003.
- 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. 2002;94:855-857.
- Wolff AC, Hammond ME, Schwartz JN, et al; American Society of Clinical Oncology; College of American Pathologists. American Society of Clinical Oncology/College of American Pathologists guideline recommendations for human epidermal growth factor receptor 2 testing in breast cancer. J Clin Oncol. 2007 Jan 1;25(1):118-145.
- Sauter G, Lee J. Bartlett JM, et al. Guidelines for human epidermal growth factor receptor 2 testing: biologic and methodologic considerations. J Clin Oncol. 2009 Mar 10;27(8):1323-1333.
- Middleton LP, Price KM, Puig P, Heydon LJ, Tarco E, Sneige N, Barr K, Deavers MT. Implementation of American Society of Clinical Oncology/College of American Pathologists HER2 Guideline Recommendations in a Tertiary Care Facility Increases HER2 Immunohistochemistry and Fluorescence In Situ Hybridization Concordance and Decreases the Number of Inconclusive Cases. Arch Pathol Lab Med. 2009; 133:775-780.
- Grimm E, Schmidt RA, Swanson PE, and Allison KH. Achieving 95% IHC/FISH Concordance for HER2: Causes and Implications of Discordant Cases. Paper presented at: USCAP Conference; March 9-11, 2009; Boston, Massachusetts.
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