Immunohistochemical Determination of HER-2/neu Expression in Invasive Breast Carcinoma

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1 Anatomic Pathology / HER-2/NEU IN BREAST CARCINOMA Immunohistochemical Determination of HER-2/neu Expression in Invasive Breast Carcinoma Russell Vang, MD, 1 Linda D. Cooley, MD, 1 Wilbur R. Harrison, MS, 1 Tommy Reese, 2 and Jacki Abrams, MD 1,2 Key Words: HER-2/neu; C-erbB2; Immunohistochemistry; FISH; Fluorescence in situ hybridization; Breast carcinoma Abstract Numerous methods exist for HER-2/neu assessment; however, technical and interpretive standardization is virtually absent. We evaluated 2 commercially available antibodies on routinely fixed paraffin-embedded tissue sections to establish our own guidelines. Thirty-three cases of infiltrating breast carcinoma were evaluated simultaneously with monoclonal and polyclonal antibodies. Only membranous staining, no matter how focal, was considered positive. An additional 32 tumors were studied subsequently using only the polyclonal antibody. Of all carcinomas, 13.0% showed immunohistochemical evidence of HER-2/neu overexpression. High-grade tumors were more often positive. There was no HER-2/neu gene expression in the benign epithelium that generally was present in the tissue section or in any of the well-differentiated tumors tested. The polyclonal antibody proved more sensitive than the monoclonal antibody. While true cytoplasmic staining was present occasionally, it did not create substantial difficulty in interpretation. The polyclonal antibody cost substantially less than the monoclonal antibody. Fluorescence in situ hybridization assay for HER-2/neu gene amplification performed on 32 of 65 cases showed concordant results in 31 cases. The immunohistochemical assay for HER-2/neu gene overexpression, using our methods, is accurate, economic, and easily integrated into the laboratory. Neu is a proto-oncogene that encodes a 185-kd protein that shares homology with epidermal growth factor receptor. Cloned from complementary DNA, it is referred to as HER-2, and cloned from genomic DNA, it is referred to as c-erbb-2; the 2 designations are used interchangeably in the literature. One copy of the gene resides on each chromosome 17 at band q21 and is thought to have a role in cell motility. The gene is amplified and the protein overexpressed in carcinomas, particularly those of the breast. The protein has 3 components, an external domain, a transmembranous portion, and an internal domain. 1 The prognostic significance of HER-2/neu amplification in breast cancer has been the subject of debate for years. Ali et al 2 concluded that c-erbb-2 amplification had no independent prognostic value compared with traditional factors, while others have demonstrated the prognostic value of HER-2/neu amplification in metastatic disease. 3 More recent studies show that HER-2/neu overexpression has therapeutic implications in infiltrating breast cancer. Trastuzumab (Herceptin), a monoclonal antibody against the p185 HER-2/neu protein (recently approved by the US Food and Drug Administration [FDA]), has therapeutic efficacy in HER-2/neu-overexpressing tumors. 4 Tumor responsiveness to tamoxifen and traditional chemotherapy also is influenced by HER-2/neu overexpression Laboratory methods for assessing HER-2/neu amplification or HER-2/neu overexpression include Southern, Northern, and Western blot techniques; immunohistochemistry, and, recently, fluorescence in situ hybridization (FISH). However, there is no clear standardization for HER-2/neu testing. The recently FDA-approved HercepTest (DAKO, Carpinteria, CA) is a move toward standardization. The goal of our study was to develop an American Society of Clinical Pathologists Am J Clin Pathol 2000;113:

2 Vang et al / HER-2/NEU IN BREAST CARCINOMA accurate cost-effective assay that is easily incorporated into the surgical pathology laboratory. Materials and Methods A total of 216 breast tumors were examined for HER- 2/neu protein overexpression by immunohistochemical methods. Initially, 33 intermediate- or high-grade (Elston- Ellis method 13 ) infiltrating breast carcinomas were assessed. Formalin-fixed paraffin-embedded tissue was evaluated using 2 commercially available antibodies, PC-11 (polyclonal, 1:3000, Novocastra, Burlingame, CA) and TAB-250 (monoclonal, 1:10, Zymed, South San Francisco, CA). When the monoclonal antibody was depleted, 32 additional consecutively accessioned tumors (all grades) were evaluated by the polyclonal antibody alone. After evaluation of the results from the first 65 tumors, 14 we studied an additional 151 tumors using the polyclonal antibody with correlation of results with histologic type and grade. The avidin-biotin-complex method was used, and all reactions were performed at room temperature. 15 Briefly, tissue sections were deparaffinized and hydrated with distilled water. Slides were quenched with 30% methanolic hydrogen peroxide for 5 minutes and then placed in phosphate-buffered saline (PBS), ph 7.6. Blocking solution was applied for 20 minutes, followed by incubation with the primary antibody for 1 hour. Slides received a 5-minute PBS rinse before application of a biotinylated secondary antibody for 30 minutes and a second 5-minute PBS rinse. Vectastain ABC working reagent (Vector Laboratories, Burlingame, CA) was added for 30 minutes followed by a 5-minute PBS rinse. Slides were developed with 3,3 diaminobenzidine for 2 to 5 minutes, rinsed in distilled water for 5 minutes, counterstained with Richard-Allen hematoxylin for 45 seconds, and rinsed again with distilled water. After a 5-second dip in 1% acid alcohol, slides were rinsed in distilled water, placed in Richard-Allen bluing reagent for 5 seconds, rinsed with tap water, and dehydrated, and coverglasses were applied. Comedo ductal carcinoma in situ was used as a positive control. Dilutions were adjusted to minimize background staining and maximize membranous staining present in the comedo ductal carcinoma in situ. Although neither antibody manufacturer recommended antigen retrieval, heat-induced epitope retrieval using citrate buffer, ph 6.0, or EDTA (1- mmol/l concentration, ph 8.0), with microwaving, was tried but neither seemed to enhance staining of the control sections. For test cases, HER-2/neu protein overexpression was considered present when any percentage of the infiltrating component showed definitive membranous staining. 16 Thirty-two of the first 65 tumors were studied using the FDA-approved FISH assay (ONCOR, Gaithersburg, MD) to detect HER-2/neu gene amplification. This was done in a blinded fashion to validate the accuracy and sensitivity of the immunohistochemical results. Three groups of tumors were evaluated: 9 high-grade carcinomas (8 poorly and 1 moderately differentiated) that were positive by immunohistochemistry, 11 high-grade carcinomas (8 poorly and 3 moderately differentiated) that were negative by immunohistochemistry, and 12 well-differentiated carcinomas that were negative by immunohistochemistry. Nine of the negative cases selected for FISH showed cytoplasmic staining that was not considered background. Amplification of the HER-2/neu gene was considered present whenever an average of more than 4 signals was counted per nucleus. However, in selected tumors, a chromosome 17 centromeric DNA probe was hybridized simultaneously with the HER-2 probe to determine chromosome 17 copy number and distinguish true amplification from chromosome aneuploidy Image 1. Results Membranous staining was interpreted as positive for overexpression of the HER-2/neu protein product. While the majority of tumors showed staining in more than 50% of the infiltrating component, focal staining also was interpreted as positive Image 2. The overall quality of staining was similar between the polyclonal and monoclonal anti- Image 1 HER-2/neu gene amplification by fluorescence in situ hybridization; blue nuclei show 2 red chromosome 17 signals and many green HER-2/neu signals ( 1,000). 670 Am J Clin Pathol 2000;113: American Society of Clinical Pathologists

3 Anatomic Pathology / ORIGINAL ARTICLE Image 2 Membranous pattern of HER-2/neu protein overexpression ( 200). bodies. Some tumors showed nonbackground cytoplasmic staining, but this alone was not considered positive Image 3. No membranous staining was noted in the nonneoplastic epithelium in any tumor. In the 33 high-grade tumors used for the initial antibody study, a higher percentage of tumors with overexpression was detected with the polyclonal antibody (10/33, [30%]) than with the monoclonal antibody (4/33 [12%]). At the final working concentration, the polyclonal antibody cost $0.50/mL, while the monoclonal antibody cost $30.00/mL. When using only the polyclonal antibody for study of the next 32 consecutively accessioned tumors, none of the welldifferentiated tumors showed overexpression. In these 65 tumors, overexpression was detected in 2 (15%) of 13 moderately differentiated tumors and 9 (23%) of 39 poorly differentiated tumors. In the 32 tumors selected for FISH assay Table 1, several showed 4 to 10 HER-2/neu signals. Simultaneous assay with chromosome 17 and HER-2/neu probes showed only 1 tumor to have discordant immunohistochemical and FISH results. Two tumors were aneuploid with multiple copies of chromosome 17. One tumor positive by FISH and negative by immunohistochemical testing showed focal immunoreactivity in additional tissue sections studied with immunohistochemistry. Because there was an admixture of the in situ and infiltrating components of this tumor, localization of the immunoreactivity was difficult. None of the tumors that showed only cytoplasmic staining were positive by FISH. Correlation between immunohistochemical and FISH results was 97%. Twenty-two cases, in which there Image 3 HER-2/neu protein overexpression by immunohistochemistry. Nonspecific cytoplasmic and true membranous staining are shown ( 400). was no amplification by FISH, were subsequently subjected to heat-induced epitope retrieval before the aforementioned immunohistochemical procedure. There was increased cytoplasmic staining, but no additional positive cases with membranous staining were detected. We assayed 216 consecutive breast tumors, 33 with both monoclonal and polyclonal antibodies and 183 with polyclonal antibody alone. The overall incidence of HER- 2/neu overexpression in the present study was 13.0% (28/216). Breakdown by histologic grade and type is shown in Table 2. Discussion Amplification of the HER-2/neu gene or overexpression of the protein has been shown to have variable prognostic significance for women with infiltrating breast carcinoma. 2,3,17,18 Breast carcinomas that overexpress HER-2/neu are unresponsive to hormonal therapy, eg, tamoxifen, and require a more intense regimen of traditional chemotherapy for effective treatment A new FDA-approved drug, trastuzumab, is specific for treatment of breast tumors with overexpression of HER-2/neu. 4,8 Because of this new focus on the treatment of women with breast cancer, pathologists and oncologists need an accurate and cost-effective test for HER-2/neu gene expression to determine the most appropriate therapy for individual patients. Earlier methods for detecting HER-2/neu overexpression were Southern, Northern, and Western blot techniques. American Society of Clinical Pathologists Am J Clin Pathol 2000;113:

4 Vang et al / HER-2/NEU IN BREAST CARCINOMA Table 1 HER-2/neu Results by Immunohistochemistry (IHC) and Fluorescence In Situ Hybridization (FISH) Interpretation Case No. IHC FISH Chromosome 17* Copy No. HER-2/neu Copy No. 1 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND > ND > ND > ND > > ND, not done; +, positive;, negative. * Chromosome 17 probe used selectively. Table 2 Type, Grade, and HER-2/neu Status of 216 Tumors * Total HER-2/neu Positive Histologic type Ductal 185 (85.6) 27 (14.6) Mixed ductal/lobular 10 (4.6) 1 (10) Lobular, classic 8 (3.7) 0 (0) Tubular 4 (1.9) 0 (0) Mucinous 4 (1.9) 0 (0) Metaplastic (sarcomatoid) 2 (0.9) 0 (0) Cribriform 1 (0.5) 0 (0) Micropapillary 1 (0.5) 0 (0) Papillary 1 (0.5) 0 (0) Histologic grade Well-differentiated 56 (26.2) 0 (0) Moderately differentiated 66 (30.8) 4 (6) Poorly differentiated 92 (43.0) 23 (25) Nuclear grade Low 28 (13) 0 (0) Intermediate 96 (44.4) 6 (6) High 92 (42.6) 22 (24) * Data are given as number (percentage). Insufficient tumor material to assign histologic grade in 2 tumors. Limitations of these molecular techniques are insensitivity to low levels of amplification owing to the dilutional effect of nonneoplastic tissue within a given sample and an inability to distinguish overexpression of an in situ from an infiltrating carcinoma. Disadvantages are the required technical expertise and expense. Conversely, immunohistochemical methods offer the advantage of direct visualization of the cell type with protein overexpression. Immunohistochemistry for HER-2/neu expression, however, has yet to be standardized. Published frequencies of HER-2/neu overexpression in breast cancers range from 14% to 89%. 19,20 The recent development and FDA approval of the HercepTest was the first attempt at standardization of the immunohistochemical method. The HercepTest uses a polyclonal antibody (DAKO), and interpretation of the assay is based on patient response to the drug Herceptin determined in the Herceptin Phase 2 clinical trial. 4,21 Problems with this test are addressed elsewhere. 22,23 While the specificity of the DAKO antibody was well documented by multiple sophisticated molecular methods, 24 the criteria for interpretation of overexpression were based on a subjective scoring system defined primarily by intensity of membranous staining. 4 In our experience, staining intensity in immunohistochemistry assays depends on a number 672 Am J Clin Pathol 2000;113: American Society of Clinical Pathologists

5 Anatomic Pathology / ORIGINAL ARTICLE of factors and can be extremely variable. The accuracy is reliable only when tissues are fixed, processed, and assayed together, thus controlling for reagent variability and other conditions that may alter staining intensity. The HercepTest, while FDA approved, has not been shown to be superior to other immunohistochemical methods and is substantially more expensive for the laboratory at $40 per test (kit price, $1,225). FISH is a method for direct visualization of HER-2/neu gene amplification. Results correlate with immunohistochemistry and other techniques. 25,26 Ratcliffe et al 27 concluded that FISH was no more sensitive than immunohistochemistry on formalin-fixed tissue. They and others 26 were unable to demonstrate HER-2/neu gene amplification by FISH in the absence of HER-2/neu protein overexpression by immunohistochemistry. In our study, we used FISH to evaluate the accuracy and sensitivity of our immunohistochemical methods. The overall incidence of HER-2/neu protein overexpression by immunohistochemistry in the 216 tumors we have studied thus far is 13.0%. This is substantially lower than the 25% to 30% rate of some studies. 3,20,27-29 Of all breast cancers in the present study, the only histologic type that seems to show overexpression is infiltrating ductal carcinoma. If we eliminate the better prognosis special type tumors, well-differentiated infiltrating ductal carcinomas, and classic pure infiltrating lobular carcinomas, our incidence of overexpression (17%) is comparable to that of other studies. 16,17,30 As newer antibodies are developed, sensitivity and specificity for the detection of HER-2/neu overexpression by this technique undoubtedly will improve, as it has in the immunohistochemical determination of estrogen and progesterone receptors. 31 The HER-2/neu oncoprotein is a transmembrane protein. Therefore, the immunohistochemical staining of the HER-2/neu protein is present in the cell membrane. Staining of the membrane represents true protein overexpression, and any percentage of positive cells is considered important. Cytoplasmic staining, when present, should never be interpreted as positive. Positive and negative control samples must be processed simultaneously with the unknown patient sample. Normal nonneoplastic breast epithelium, when present, should serve as an internal negative control. 32 In the present study, we compared 2 commercially available antibodies to determine which was better for immunohistochemical assessment of the HER-2/neu protein overexpression. We validated the immunohistochemical results by FISH and showed excellent correlation. We concluded the following: (1) While the FISH assay is accurate, the cost of the FISH DNA probe and the special expertise required to perform FISH analysis makes immunohistochemistry the most cost-effective method currently available for assessing HER-2/neu. (2) The polyclonal antibody by Novocastra is superior to the monoclonal antibody by Zymed with respect to sensitivity and cost. (3) HER-2/neu overexpression, determined by immunohistochemistry, correlates with tumor grade. (4) Provided that adequate internal and external controls are used and interpretation is made from cell membrane staining, immunohistochemistry is one of the most accurate and reliable methods available. From 1 The University of Texas Medical School and 2 St Luke s Episcopal Hospital, Houston, TX. Presented in part as an abstract poster at the March 1999 United States and Canadian Academy of Pathology Meeting in San Francisco, CA. Address reprint requests to Dr Abrams: St Luke s Episcopal Hospital, Dept of Pathology, 6720 Bertner St, MC4-265, Houston, TX Acknowledgments: We thank Anwar Farhood, MD, Houston, TX, and Hector Battifora, MD, Cypress, CA, for their critical review and helpful comments, and Eric Bernicker, MD, our clinical oncology colleague who inspired this study. References 1. De Potter CR, Schelfhout A-M. The neu-protein and breast cancer. Virchows Arch. 1995;426: Ali IU, Campbell G, Libereau R, et al. Lack of evidence for the prognostic significance of c-erbb-2 amplification in human breast carcinoma. Oncogene Res. 1988;3: Slamon DJ, Godolphin W, Jones LA, et al. Studies of the HER-2/neu proto-oncogene in human breast and ovarian cancer. Science. 1989;244: Pegram MD, Lipton A, Hayes DF, et al. 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