Assessment of Her-2/neu gene amplification status in breast carcinoma with equivocal 2+ Her-2/neu immunostaining

Background and purpose: Amplification of Her-2/neu gene occurs in 25-30% of breast carcinomas. FDA approved trastuzumab (Herceptin) is effective only in tumors having the gene amplification. Immunohistochemistry (IHC) for Her-2/neu protein is widely used but false positive and false negative results exist. Fluorescence in-situ hybridization (FISH) has both excellent sensitivity and specificity in detecting Her-2/neu amplification. Comparative studies have shown discordant results in proportion of cases with equivocal 2+ immunostain. This study is thus conducted to ascertain the frequency of Her-2/neu gene amplification by FISH in breast carcinoma specified as score 2+ by IHC and to correlate these findings with parameters of prognosis in breast cancer. Methods: From October 2008 till May 2010 all paraffin blocks from cases with invasive breast carcinoma which were scored as 2+ by IHC were eligible for the study, there were 50 cases. Immunohistochemical evaluation of Her-2/neu was performed using the HercepTest. All cases were immunohistochemically evaluated for ER and PR. FISH was performed using FDA approved Path-Vysion Her-2/neu/CEP 17 dual color probe. Results: Nine cases (18%) out of 50 cases scored as Her-2/neu 2+ by IHC showed true gene amplification with a median value of scoring ratio 4.28 ranging from 2.37 to 13.26. Another two cases showed low level of amplification but when corrected for Her-2/neu/CEP ratio they did not show true amplification as they were associated with polysomy 17. With the exception of tumor size, neither patient's age, histologic grade nor lymph node status were correlated with Her-2/neu gene amplification. Significant inverse correlation existed between Her-2/neu gene amplification and ER (P = 0.01), PR status (P < 0.001). Conclusion: Even though FISH is a more complex and expensive procedure, it should be considered the method of choice for assessment of Her-2/neu gene status especially for equivocal cases by IHC that are not accompanied by true gene amplification in the majority of breast carcinoma cases. (C) 2011 National Cancer Institute, Cairo University. Production and hosting by Elsevier B.V.