Amplification of the TOP2A gene does not predict high levels of topoisomerase II alpha protein in human breast tumor samples.
Recent clinical trials have suggested that patients whose breast tumors overexpress HER2 may derive particular benefit from anthracycline-containing chemotherapy compared to that without anthracycline. It has been proposed that the HER2 gene amplification reported in these tumors might mask an underlying TOP2A gene amplification that occurs frequently and concurrently with HER2 amplification. Topoisomerase II alpha, encoded by TOP2A, is a direct molecular target of anthracycline drug action and is potentially useful as a predictive marker of response to anthracycline therapy for breast cancer. In this study, we examined whether TOP2A gene amplification is an appropriate marker for identifying breast tumors expressing high levels of topoisomerase II alpha. We determined topoisomerase II alpha protein expression by immunohistochemistry in 81 human breast tumors in relation to HER2 and TOP2A gene copy numbers analyzed by fluorescence in situ hybridization, histologic grade, cell proliferation fraction measured by MIB-1 expression, and HER2 protein expression determined by immunohistochemistry. The results showed no correlation between TOP2A gene copy number and topoisomerase II alpha protein expression levels in breast tumors, in contrast to the analogous situation for HER2 gene amplification and HER2 immunohistochemistry. Our results suggest that TOP2A gene amplification in breast tumors does not predict high expression of topoisomerase II alpha protein.
Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada.
Rosemary E
RE
Mueller
Robert K
RK
Parkes
Irene
I
Andrulis
Frances P
FP
O'Malley
D000951:Antigens, Neoplasm; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D002886:Chromosomes, Human, Pair 17 / Q000235:genetics; D004250:DNA Topoisomerases, Type II / Q000235:genetics* / Q000276:immunology; D004268:DNA-Binding Proteins; D003627:Data Interpretation, Statistical; D005557:Formaldehyde / Q000378:metabolism; D005784:Gene Amplification / Q000235:genetics*; D018628:Gene Dosage; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods / Q000706:statistics & numerical data; D017404:In Situ Hybridization, Fluorescence / Q000379:methods; D019394:Ki-67 Antigen / Q000276:immunology; D016612:Paraffin Embedding / Q000379:methods; D011003:Ploidies; D000075223:Poly-ADP-Ribose Binding Proteins; D011237:Predictive Value of Tests; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000096:biosynthesis / Q000276:immunology; D016707:Tissue Fixation / Q000379:methods
D000951:Antigens, Neoplasm; D004250:DNA Topoisomerases, Type II; D004268:DNA-Binding Proteins; D005557:Formaldehyde; D019394:Ki-67 Antigen; D000075223:Poly-ADP-Ribose Binding Proteins; D018719:Erb-b2 Receptor Tyrosine Kinases; C000618811:TOP2A protein, human