|
Advertisement |
|
|
||
 |
|
|||||
|
|||||
|
 |
||||||
|
||||||
|
||||||
|
Originally published as JCO Early Release 10.1200/JCO.2008.17.2684 on September 15 2008 © 2008 American Society of Clinical Oncology.
Polysomy 17 and HER-2 Amplification: True, True, and Unrelated
Department of Medicine, Boston University Medical Center, Boston, MA Approximately 25% of breast cancers overexpress the human epidermal growth factor receptor 2 (HER-2) protein, usually as a result of high copy number of its gene (amplification) on chromosome 17q12-21. HER-2 signaling promotes cell proliferation, and overexpression or gene amplification are associated with poor prognosis.1 In view of this, trastuzumab (Herceptin; Genentech, South San Francisco, CA), a humanized monoclonal immunoglobulin G antibody, was developed to specifically target the extracellular domain of HER-2.2 Because trastuzumab is both effective and toxic in some patients, identifying patients who will benefit is of great importance. Currently, patient selection is based on the determination of HER-2 status, because trastuzumab is expected to be effective only against HER-2–positive breast cancers. The definition of HER-2 positive has evolved over time, and guidelines to standardize testing and interpretation have been proposed.3,4 Even with such guidelines, patient selection for HER-2–targeted therapy can sometimes be controversial. HER-2 testing contains some inherent variability and can yield accurate but potentially equivocal results. In addition, genetic or biologic heterogeneity among tumors and patients plays a role in response. The article by Vanden Bempt et al5 in this issue of Journal of Clinical Oncology highlights one aspect of this important issue by showing that tumors with increased HER2 gene copy number as a result of extra copies of chromosome 17 (polysomy 17) resemble HER-2–negative tumors, rather than tumors with HER2 gene amplification. Polysomy 17 tumors do not overexpress HER-2 mRNA or protein, and they cannot be distinguished from HER-2–negative tumors by standard pathologic criteria, including tumor grade and hormone receptor status. This finding should influence the interpretation of HER-2 test results and could eventually improve selection of patients for HER-2–targeted treatment. HER-2 status is determined by one of two approaches: estimation of protein expression by immunohistochemistry (IHC) or measurement of gene copy number by fluorescent in situ hybridization (FISH). Correlation between the two approaches is high, but not perfect. Concordance between different laboratories’ results varies, primarily when measuring IHC. Variability in IHC can result from different tissue preparation and staining procedures, scoring criteria, tissue sampling, and the inherently subjective and semi-quantitative nature of IHC interpretation (scored as 0, 1+, 2+, 3+). FISH is more quantitative and reproducible, but two different scoring systems are used: one counts the total number of HER2 genes per nucleus, and the other uses dual probes to count each nucleus’ ratio of HER2 genes to chromosome 17 centromeres (HER2/CEP17). This ratio distinguishes increased HER2 gene copy number secondary to HER2 gene amplification from increased HER2 gene copy number secondary to extra copies of chromosome 17. Extra copies are common because breast cancer genomes are often aneuploid. The recent guidelines suggest three acceptable alterative methods and criteria for defining HER-2 status as positive, equivocal, or negative: absolute HER2 gene copy number (positive is > six), HER2/chromosome 17 ratio (positive is > 2.2), or IHC (positive is intense staining in > 30% of tumor cells [3+]).3,4 What to do with equivocal results, such as absolute copy numbers between four and six or ratios between 1.8 and 2.2, remains uncertain. At least two genetic mechanisms can generate increased HER2 gene copy number. The increase is usually due to gene amplification, a process that occurs through preferential replication of a segment of a chromosome, named the amplicon. The genetic events producing gene amplifications are complex and may include telomere shortening, repeated breakage-fusion-bridge cycles, and incorporation of sequences from multiple chromosomes. The HER2 amplicon varies in size and in number of replicates but encompasses multiple genes, some of which are also dysregulated and could participate in cancer initiation or progression.
In contrast to gene amplification, aneuploidy is a change in the number of whole chromosomes. It is sometimes known as chromosome instability. Changes in chromosome number are usually a consequence of mis-segregation during mitosis. Aneuploidy involving chromosome 17, usually with increased copies (polysomy), is seen in approximately one third of breast cancers (range, approximately 10% to 50%, depending on which tumors are assessed and which criteria are applied). The copy number can vary, and tumors are often grouped as low ploidy (three to four copies) or the far less common high ploidy ( Although amplification is by far the most common mechanism generating excess HER2 gene copies, polysomy occurs frequently. This has raised the question of whether increased HER-2 protein expression can result not only from gene amplification, but also from increased number of chromosome 17. The consequence would then be that patients with polysomy 17 tumors might be candidates for trastuzumab. Several groups have considered the potential effects of chromosome 17 polysomy on HER2 gene expression. Polysomy 17, without HER2 gene amplification, does not seem to significantly increase HER2 mRNA.6,7 However, polysomy 17 alone may increase HER-2 protein expression.6-14 Most studies find little IHC 3+ expression (although very high ploidy may be associated with IHC 3+). But IHC 2+ expression is common in polysomy 17 tumors lacking HER2 gene amplification, although no more than half of IHC 2+ tumors seem to have polysomy 17. In addition, some series link polysomy 17 tumors with histologic features or outcome, but no consensus associations have emerged.6,12,15,16 These findings have generated discussion about the accurate classification of tumors with polysomy 17 unassociated with HER2 gene amplification. Vanden Bempt et al5 ask whether tumors with polysomy 17, but lacking HER2 gene amplification, should be considered HER-2 negative or positive. The answer seems to be that they are functionally HER-2 negative. The authors examined 226 invasive breast cancers for HER-2 status using dual-probe FISH, mRNA level, and protein expression. The results were interpreted according to the recommended guidelines.4 Polysomy 17 cancers, with and without HER2 gene amplification, were distinguished. This comprehensive analysis confirms that cancers with polysomy 17 without HER2 gene amplification do not overexpress HER2 mRNA and do not overexpress protein at the significant IHC 3+ level. The authors also compared tumor HER-2 status with pathologic features. For every variable considered (grade, size, lymph node involvement, lymphovascular invasion, and estrogen and progesterone receptor expression), the polysomy 17 tumors without HER2 amplification resemble HER-2–negative tumors. Polysomy 17 tumors without HER2 gene amplification may not be identical to HER-2–negative tumors, although nearly three fourths had 2+ IHC staining, a larger proportion than usually reported in HER-2–negative tumors. Because only five cancers seemed to have had high ploidy, HER2 copy number did not seem to be associated with level of expression (although the authors do not report the high ploidy cases separately). All equivocal FISH results could be explained by polysomy 17. Finally, overall survival of patients with polysomy 17 tumors was intermediate between the HER2-amplified and HER2-unamplified groups. It should be noted, however, that these 226 cases are heterogeneous and were not treated uniformly, so it is important not to overinterpret this finding. These results suggest that tumors with extra copies of HER2 as a result of polysomy 17 are fundamentally different than tumors with HER2 amplification. Extra copies of the HER2 gene in a seemingly normal context on chromosome 17 are not associated with increased mRNA or protein, in contrast to what occurs with gene amplification. Although the available data are somewhat limited, the number of gene copies does not seem to matter greatly, perhaps because HER-2 remains normally regulated. In contrast, the processes leading to amplification must somehow dysregulate the expression of HER-2 and perhaps produce additional detrimental alterations. The distinction between these two tumor subtypes supports use of a dual-probe assay as the method of choice in clinical practice to identify functionally HER-2–overexpressing tumors. At present, there is no clinical indication to determine chromosome 17 ploidy by itself. In addition, the article by Vanden Bempt et al5 raises the question of whether there is any role for trastuzumab in treatment of polysomy 17 tumors. This question has not been directly studied, but polysomy 17 tumors’ similarity to HER-2–negative tumors suggests that they would be unlikely to respond to trastuzumab. This is consistent with studies reporting response to trastuzumab only in tumors with gene amplification or IHC 3+ staining.17 It is conceivable, however, that a subset of polysomy 17 tumors could respond to trastuzumab, for example, in tumors with high ploidy. A recent study has reported response to trastuzumab monotherapy in two polysomy 17 HER2-unamplified tumors,13 but both tumors stained IHC 3+ and had high ploidy. None of the polysomy 17 tumors in the study by Vanden Bempt et al5 demonstrated IHC 3+ staining, but they had few high-ploidy tumors and also used the recently recommended, higher cutoff for IHC 3+.
If trastuzumab benefits any polysomy 17 tumors, factors other than HER-2 expression will likely influence response, and the magnitude of benefit may be different than in HER-2–positive tumors. Targeted therapy doesn't always work exactly as predicted. Truly HER-2–negative tumors are unlikely to respond to HER-2–directed therapy (although there is some recent disagreement), but only half of HER-2–positive tumors respond to trastuzumab. Prediction of response is suboptimal.18 Biomarkers or mediators of response that have been considered include factors related to HER-2 (activation status, cleaved extracellular domain in the serum, dimerization partner HER-1, downstream signaling pathways), coamplification of cMYC,19 and absolute HER2 gene copy number (although the predictive data are sparse20,21). Immune factors also play a role; for example, an individual's particular Fc Many avenues of investigation exist; prioritizing them is a challenge. Basic investigations of the HER-2 amplicon and of aneusomy are paramount. More complete understanding of factors modifying response to particular HER-2–directed treatments is critical. Determining whether HER-2–targeted treatments are effective in polysomy 17 tumors is of great clinical relevance. New trials to directly test this question may not be the most efficient approach. Alternatively, review or reanalysis of IHC, FISH, and response data from existing trials could determine whether any polysomy 17 HER-2–unamplified tumors respond to trastuzumab or lapatinib. For instance, it would be of interest to determine whether polysomy 17 HER-2–unamplified tumors were classified differently in the trials that produced contradictory results about HER-2–negative tumor response to trastuzumab. Polysomy 17 HER2-unamplified tumors may have been considered HER-2–negative in National Surgical Adjuvant Breast and Bowel Project Trial B-31, which found that adjuvant trastuzumab benefited patients with HER-2–negative tumors.23,24 These tumors may have been considered HER-2 positive in the Cancer and Leukemia Group B trial, which did not demonstrate benefit from the addition of trastuzumab to paclitaxel in HER-2–negative tumors.25 If this is the case, it might partially reconcile the disparate results. Another promising area of investigation is the role of polysomy 17, as well as HER2 amplification, in preinvasive cancers, both alone and in association with invasive disease. Carcinomas in situ express HER-2 at least as often as invasive cancers, but expression can be heterogeneous within a tumor and is more common in, but not exclusive to, high-grade lesions.26,27 The cause of HER-2 overexpression in carcinomas in situ and how it relates to HER-2 expression in invasive cancers is poorly understood. This research would dovetail with a new development in HER-2–directed therapy; vaccines targeting HER-2 are being successfully studied in high-risk ductal carcinoma in situ.28-30 Vanden Bempt et al5 demonstrate that polysomy 17 HER2 gene unamplified tumors are pathologically indistinguishable from HER-2–negative tumors, although they often express low to moderate levels of HER-2. This suggests that tumors with extra copies of HER2 as a result of polysomy 17 are fundamentally different from tumors with extra copies resulting from gene amplification; it is not at all clear that they would benefit from existing HER-2–targeted therapies. Basic genetic and pharmacologic studies, review of existing clinical trial data, and investigation of HER-2 alterations early in breast cancer development will produce more accurate selection of patients for targeted treatment and more successful outcomes. AUTHOR'S DISCLOSURES OF POTENTIAL CONFLICTS OF INTEREST The author(s) indicated no potential conflicts of interest. NOTES published online ahead of print at www.jco.org on September 15, 2008 REFERENCES
1. 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 235:177-182, 1987 2. Hudis CA: Trastuzumab: Mechanism of action and use in clinical practice. N Engl J Med 357:39-51, 2007 3. Wolff AC, Hammond ME, Schwartz JN, et al: American Society of Clinical Oncology/College of American Pathologists Guideline Recommendations for Human Epidermal Growth Factor Receptor 2 Testing in Breast Cancer. Arch Pathol Lab Med 131:18, 2007[Medline] 4. Wolff AC, Hammond ME, Schwartz JN, et al: 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 25:118-145, 2007 5. Vanden Bempt I, Van Loo P, Drijkoningen M, et al: Polysomy 17 in breast cancer: Clinicopathologic significance and impact on HER-2 testing. J Clin Oncol doi:10.1200/JCO.2007.13.4296 [epub ahead of print on September 15, 2008] 6. Dal Lago L, Durbecq V, Desmedt C, et al: Correction for chromosome-17 is critical for the determination of true Her-2/neu gene amplification status in breast cancer. Mol Cancer Ther 5:2572-2579, 2006 7. Downs-Kelly E, Yoder BJ, Stoler M, et al: The influence of polysomy 17 on HER2 gene and protein expression in adenocarcinoma of the breast: A fluorescent in situ hybridization, immunohistochemical, and isotopic mRNA in situ hybridization study. Am J Surg Pathol 29:1221-1227, 2005[CrossRef][Medline] 8. Bose S, Mohammed M, Shintaku P, et al: Her-2/neu gene amplification in low to moderately expressing breast cancers: Possible role of chromosome 17/Her-2/neu polysomy. Breast J 7:337-344, 2001[CrossRef][Medline] 9. Lal P, Salazar PA, Ladanyi M, et al: Impact of polysomy 17 on HER-2/neu immunohistochemistry in breast carcinomas without HER-2/neu gene amplification. J Mol Diagn 5:155-159, 2003 10. Ma Y, Lespagnard L, Durbecq V, et al: Polysomy 17 in HER-2/neu status elaboration in breast cancer: Effect on daily practice. Clin Cancer Res 11:4393-4399, 2005 11. Varshney D, Zhou YY, Geller SA, et al: Determination of HER-2 status and chromosome 17 polysomy in breast carcinomas comparing HercepTest and PathVysion FISH assay. Am J Clin Pathol 121:70-77, 2004[CrossRef][Medline] 12. Salido M, Tusquets I, Corominas JM, et al: Polysomy of chromosome 17 in breast cancer tumors showing an overexpression of ERBB2: A study of 175 cases using fluorescence in situ hybridization and immunohistochemistry. Breast Cancer Res 7:R267-R273, 2005[CrossRef][Medline] 13. Hofmann M, Stoss O, Gaiser T, et al: Central HER2 IHC and FISH analysis in a trastuzumab (Herceptin) phase II monotherapy study: Assessment of test sensitivity and impact of chromosome 17 polysomy. J Clin Pathol 61:89-94, 2008 14. Hyun CL, Lee HE, Kim KS, et al: The effect of chromosome 17 polysomy on HER-2/neu status in breast cancer. J Clin Pathol 61:317-321, 2008 15. Torrisi R, Rotmensz N, Bagnardi V, et al: HER2 status in early breast cancer: Relevance of cell staining patterns, gene amplification and polysomy 17. Eur J Cancer 43:2339-2344, 2007[CrossRef][Medline] 16. Watters AD, Going JJ, Cooke TG, et al: Chromosome 17 aneusomy is associated with poor prognostic factors in invasive breast carcinoma. Breast Cancer Res Treat 77:109-114, 2003[CrossRef][Medline] 17. 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 18. Singer CF, Köstler WJ, Hudelist G: Predicting the efficacy of trastuzumab-based therapy in breast cancer: Current standards and future strategies. Biochim Biochim Biophys Acta [epub ahead of print on March 4, 2008] 19. Kim C, Bryant J, Horne Z, et al: Trastuzumab sensitivity of breast cancer with co-amplification of HER2 and cMYC suggests pro-apoptotic function of dysregulated cMYC in vivo. Breast Cancer Res Treat 94:S6, 2005 (abstr 46) 20. Esteva FJ, Wang J, Lin F, et al: CD40 signaling predicts response to preoperative trastuzumab and concomitant paclitaxel followed by 5-fluorouracil, epirubicin, and cyclophosphamide in HER-2-overexpressing breast cancer. Breast Cancer Res 9:R87, 2007[CrossRef][Medline] 21. Tubbs RR, Pettay JD, Prescott N, et al: Does HER2 gene amplification copy number predict clinical response to herceptin? A fluourescence and silver in situ hybridization study. Breast Cancer Res Treat 100:S52, 2006 (abstr 1041) 22. Musolino A, Naldi N, Bortesi B, et al: Immunoglobulin G fragment C receptor polymorphisms and clinical efficacy of trastuzumab-based therapy in patients with HER-2/neu-positive metastatic breast cancer. J Clin Oncol 26:1789-1796, 2008 23. Paik S, Kim C, Jeong J, et al: Benefit from adjuvant trastuzumab may not be confined to patients with IHC 3+ and/or FISH-positive tumors: Central testing results from NSABP B-31. J Clin Oncol 25:5s, 2007 (abstr 511) 24. Paik S, Kim C, Wolmark N: HER2 status and benefit from adjuvant trastuzumab in breast cancer. N Engl J Med 358:1409-1411, 2008 25. Seidman AD, Berry D, Cirrincione C, et al: Randomized phase III trial of weekly compared with every-3-weeks paclitaxel for metastatic breast cancer, with trastuzumab for all HER-2 overexpressors and random assignment to trastuzumab or not in HER-2 nonoverexpressors: Final results of Cancer and Leukemia Group B protocol 9840. J Clin Oncol 26:1642-1649, 2008 26. Allred DC, Wu Y, Mao S, et al: Ductal carcinoma in situ and the emergence of diversity during breast cancer evolution. Clin Cancer Res 14:370-378, 2008 27. Meijnen P, Peterse JL, Antonini N, et al: Immunohistochemical categorisation of ductal carcinoma in situ of the breast. Br J Cancer 98:137-142, 2008[CrossRef][Medline] 28. Disis ML, Gooley TA, Rinn K, et al: Generation of T-cell immunity to the HER-2/neu protein after active immunization with HER-2/neu peptide-based vaccines. J Clin Oncol 20:2624-2632, 2002 29. Bernhard H, Salazar L, Schiffman K, et al: Vaccination against the HER-2/neu oncogenic protein. Endocr Relat Cancer 9:33-44, 2002[Abstract] 30. Czerniecki BJ, Koski GK, Koldovsky U, et al: Targeting HER-2/neu in early breast cancer development using dendritic cells with staged interleukin-12 burst secretion. Cancer Res 67:1842-1852, 2007
Related Article
This article has been cited by other articles:
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|
|||||||||||
|
|||||||||||
|
|
Copyright © 2008 by the American Society of Clinical Oncology, Online ISSN: 1527-7755. Print ISSN: 0732-183X
|
five copies). Polysomy 17 will lead to increased HER2 gene copy number, but it is mechanistically distinct from HER2 gene amplification. The two aberrations can coexist, and it is uncertain whether they are linked or are independent. Polysomy of other chromosomes is rarely measured simultaneously. 
receptor genotype seems to modulate efficacy.
