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HER2 Testing: Summary for Breast Cancer Patients - Page 2 |
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Fluorescence in situ Hybridization (FISH) FISH is a gene-based test used to determine the number of HER2 genes in the cells of the tumor. In HER2-positive breast cancer there are too many copies of the HER2 gene, the gene is amplified. The FISH test is done by a pathologist in a laboratory on a sample of a tumor removed during a biopsy, a lumpectomy or a mastectomy. The steps in the most commonly used procedure (Pathvysion) are: * breast cancer tissue is prepared for testing * the sample of tumor (a thin slice) is exposed to fluorescent compounds (will glow under certain light) * one fluorescent compound adheres (sticks) to the HER2 genes in a cell and another adheres to chromosome 17 in a cell * when the sample is exposed to a special light the HER2 genes and chromosome 17 light up with different colors and can be counted; a pathologist or computer then reads the prepared slide * the proportion or ratio of genes to chromosomes 17 in 60 cells is determined and the average number of HER2 genes/chromosome 17 per cell is then reported * The HER2 gene/chromosome 17 ratio in a normal, nondividing cell should be 1 to 1- 1 gene on each of the 2 copies of chromosome 17; the HER2 gene/chromosome 17 ratio can increase up to 2 to 1 in cells during certain stages of normal cell division; an average HER2 gene/chromosome 17 ratio of less than 2 to 1 is reported as HER2 negative * tumor samples with an average HER2 gene/chromosome 17 ratio of greater than or equal to 2 to 1 (2.5 to 1, 3.2 to 1, etc.) are reported as HER2 positive * Another FISH procedure (INFORM) uses a similar procedure but measures only the average number of HER2 gene copies/cell; tumor samples with an average of greater than 4 HER2 gene copies/cell are considered HER2 positive.
Problems encountered in FISH testing: * Scoring problems can occur when the HER2 gene/chromosome 17 ratios are in the 1.8 to 2.2 range (Pathvysion test) or when the average number of HER2 gene copies/cell are in the range of greater than 4 to less than 6 (INFORM test); these are considered borderline amplified. * At this time no high-level evidence or agreement is available on how results in the borderline range should be interpreted or confirmed. * Scoring difficulties found with FISH testing may be associated with the specific set of cells chosen to include in the determination or tissue processing. * False positive or false negative HER2 test results can occur
NCCN RECOMMENDATIONS If appropriate quality control/assurance procedures are in place for a laboratory5, either IHC or FISH methods may be used to determine HER2 tumor status. If the laboratory does not have control/assurance procedures in place, the sample should be sent to a reference laboratory6 that does meet quality control/assurance procedures. * HER2 positive status is IHC 3+ or FISH positive * HER2 negative status is IHC 0, 1+ or FISH negative * A borderline IHC result of 2+ should be followed by performing a FISH test. * A borderline FISH result of an average HER2 gene/chromosome 17 ratio of 1.8 to 2.2 (or an average of greater than 4 to less than 6 HER2 gene copies/cell) should be followed by one of the following: * Counting additional cells in the tissue sample * Retesting with FISH * Performing an IHC test
Questions To Ask About Testing * What tests will be done on the sample of my breast cancer tumor? * Is the laboratory that will test my tumor for HER2 status accredited to perform such testing? * Has the laboratory properly validated the HER2 test(s) it uses? * Which test will be used to determine my HER2 status? * What will happen if the IHC test comes back 2+? * What will happen if the FISH test comes back with a borderline result? Romond EH, Perez EA, Bryant J, et al Trastuzumab plus adjuvant chemotherapy for operable HER2-positive breast cancer. N Engl J Med. 2005;353:1673-168 4. 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. 2001;344:783-792. 3 breastcancer.org. Herceptin Side Effects, 19 Sep 2006.http://www.breastcancer.org/herceptin_side_effects.html Carlson RW, Moench SJ, Hammond MEH et al. HER2 testing in breast cancer: NCCN Task Force report and recommendations. J Natl Compr Canc Netw.. 2006;4 suppl 3:S1-S-22. (url to be added when available online) Standards for Laboratory Accreditation . College of American Pathologists. 2000. 19 Sep 2006. http://www.cap.org/apps/cap.portal?_nfpb=true&cntvwrPtlt_actionOverride=%2Fportlets%2FcontentViewer%2Fshow&_windowLabel=cntvwrPtlt&cntvwrPtlt%7BactionForm.contentReference%7D=laboratory_accreditation%2Fstandards%2Fstandards.html&_state=maximized&_pageLabel=cntvwr 6 �Reference Laboratory. Encyclopedia of Public Health. Ed Lester Breslow, Thomson Gale, 2002. enotes.com. 2006. 19 Sep 2006. http://health.enotes.com/public-health-encyclopedia/reference-laboratory 7Your Pathology Report. breastcancer.org. http://www.breastcancer.org/pathology_intro.html (Free brochure) 8Breast Cancer Work-Up. National Comprehensive Cancer Network, American Cancer Society. 19 Sep 2006. http://www.nccn.org/patients/patient_gls/_english/_breast/3_work-up.asp
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Last Updated on Thursday, 21 January 2010 10:12 |