title: Topoisomerase 2A gene amplification in breast cancer. Critical evaluation of different FISH probes.
abstract: The HER2 amplicon on chromosome 17q is variable in size and occasionally includes Topoisomerase 2A (TOP2A) at 17q21-22. It has been suggested that TOP2 co-amplification, not HER2 amplification on chromosome 17q11.2-12, is a useful predictive marker of response to anthracycline-based chemotherapy in breast cancer patients. Given the significant toxicities of anthracyclines, the detection methods of TOP2A gene amplifications have to be standardized. We determined TOP2A gene alterations using two different fluorescence in situ hybridization (FISH) DNA probes. HER2 amplifications were identified with the PathVysion probe. TOP2A status of 42 HER2 amplified breast cancers was tested by FISH with PathVysion covering 160 kb and DAKO pharm DX covering 228 kb of the TOP2A amplicon. TOP2A protein expression was tested by immunohistochemistry. Multiplex-ligation dependent probe amplification (MLPA) was performed retrospectively in cases showing discrepancies. TOP2A was amplified in 15 of 42 cases (35%) with DAKO pharm DX and in 11 of 42 cases (26%) with PathVysion. In all four discrepant cases, MLPA showed no TOP2A amplification, but instead amplification of an upstream region including HER2. TOP2A was deleted in the same seven of 42 carcinomas (17%) with both probes. TOP2A protein expression was detected in all 42 tumours (100%) with high intratumoral heterogeneity. TOP2A amplification rate depends on the length of the hybridized probes for the TOP2A locus. Because TOP2A, not HER2, is a target of anthracyclines, non-overlapping DNA probes should be used to evaluate any associations between such alterations and response to anthracycline-based chemotherapy.
authors.affiliation: Department of Pathology, Institute of Surgical Pathology, University Hospital Zurich, Schmelzbergstrasse 12, 8091 Zurich, Switzerland. zsuzsanna.varga@usz.ch
authors.forename: Zsuzsanna
authors.initials: Z
authors.lastname: Varga
authors.forename: Cathy B
authors.initials: CB
authors.lastname: Moelans
authors.forename: Ursina
authors.initials: U
authors.lastname: Zuerrer-Hardi
authors.forename: Constanze
authors.initials: C
authors.lastname: Ramach
authors.forename: Silvia
authors.initials: S
authors.lastname: Behnke
authors.forename: Glen
authors.initials: G
authors.lastname: Kristiansen
authors.forename: Holger
authors.initials: H
authors.lastname: Moch
mesh_terms: D000951:Antigens, Neoplasm / Q000235:genetics* / Q000378:metabolism; D001943:Breast Neoplasms / Q000175:diagnosis / Q000235:genetics* / Q000378:metabolism; D015342:DNA Probes; D004250:DNA Topoisomerases, Type II / Q000235:genetics* / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D005260:Female; D005784:Gene Amplification; D018628:Gene Dosage; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D000075223:Poly-ADP-Ribose Binding Proteins; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics / Q000378:metabolism
chemical_list: D000951:Antigens, Neoplasm; D015342:DNA Probes; D004250:DNA Topoisomerases, Type II; D004268:DNA-Binding Proteins; D000075223:Poly-ADP-Ribose Binding Proteins; D018719:Erb-b2 Receptor Tyrosine Kinases; C000618811:TOP2A protein, human