Does chromosome 17 centromere copy number predict polysomy in breast cancer? A fluorescence in situ hybridization and microarray-based CGH analysis.
Approximately 8% of breast cancers show increased copy numbers of chromosome 17 centromere (CEP17) by fluorescence in situ hybridization (FISH) (ie average CEP17 >3.0 per nucleus). Currently, this pattern is believed to represent polysomy of chromosome 17. HER2-amplified cancers have been shown to harbour complex patterns of genetic aberrations of chromosome 17, in particular involving its long arm. We hypothesized that aberrant copy numbers of CEP17 in FISH assays may not necessarily represent true chromosome 17 polysomy. Eighteen randomly selected CEP17 polysomic cases and a control group of ten CEP17 disomic cases, as defined by dual-colour FISH, were studied by microarray-based comparative genomic hybridization (aCGH), which was performed on microdissected samples using a 32K tiling-path bacterial artificial chromosome microarray platform. Additional FISH probes were employed for SMS (17p11.2) and RARA (17q21.2) genes, as references for chromosome 17 copy number. Microarray-based comparative genomic hybridization revealed that 11 out of the 18 polysomic cases harboured gains of 17q with involvement of the centromere, one displayed 17q gain sparing the centromeric region, and only one could be defined as polysomic. The remaining five cases displayed amplification of the centromeric region. Among these, one case, showing score 2+ by immunohistochemistry and 8.5 HER2 mean copy number, was classified as not amplified by HER2/CEP17 ratio and as amplified by HER2/SMS ratio. Our results suggest that true chromosome 17 polysomy is likely to be a rare event in breast cancer and that CEP17 copy number greater than 3.0 in FISH analysis is frequently related to gain or amplification of the centromeric region. Larger studies investigating the genetic profiles of CEP17 polysomic cases are warranted.
Marchiò
Caterina
C
The Breakthrough Breast Cancer Research Centre-Institute of Cancer Research, London, UK.
Lambros
Maryou B
MB
Gugliotta
Patrizia
P
Di Cantogno
Ludovica Verdun
LV
Botta
Cristina
C
Pasini
Barbara
B
Tan
David S P
DS
Mackay
Alan
A
Fenwick
Kerry
K
Tamber
Narinder
N
Bussolati
Gianni
G
Ashworth
Alan
A
Reis-Filho
Jorge S
JS
Sapino
Anna
A
D001943:Breast Neoplasms / Q000235:genetics*; D002503:Centromere; D002886:Chromosomes, Human, Pair 17; D055028:Comparative Genomic Hybridization; D005260:Female; D005784:Gene Amplification; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D046228:Microarray Analysis; D011123:Polyploidy; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics; D018168:Receptors, Retinoic Acid / Q000235:genetics; D000072482:Retinoic Acid Receptor alpha
D018719:Erb-b2 Receptor Tyrosine Kinases; D018168:Receptors, Retinoic Acid; D000072482:Retinoic Acid Receptor alpha; C000607071:RARA protein, human