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Title: Monosomy of chromosome 17 in breast cancer during interpretation of HER2 gene amplification
Authors: Brunelli, Matteo
Nottegar, Alessia 
Bogina, Giuseppe 
Caliò, Anna 
Cima, Luca 
Eccher, Albino 
Vicentini, Caterina 
Marcolini, Lisa 
Scarpa, Aldo 
Pedron, Serena 
Brunello, Eleonora 
Knuutila, Sakari
Sapino, Anna
Marchiò, Caterina
Bria, Emilio
Molino, Annamaria 
Carbognin, Luisa 
Tortora, Giampaolo 
Jasani, Bharat
Miller, Keith
Merdol, Ibrahim
Zanatta, Lucia
Laurino, Licia
Wirtanen, Tiina
Zamboni, Giuseppe 
Marconi, Marcella 
Chilosi, Marco 
Manfrin, Erminia 
Martignoni, Guido 
Bonetti, Franco 
Keywords: Breast carcinoma;FISH analysis;HER 2 amplification;aCGH method;chromosome 17;double probes;false positive;monosomy;ratio (HER2/CEP 17);single signals
Issue Date: 2015
Journal: American journal of cancer research 
Monosomy of chromosome 17 may affect the assessment of HER2 amplification. Notably, the prevalence ranges from 1% up to 49% due to lack of consensus in recognition. We sought to investigate the impact of monosomy of chromosome 17 to interpretation of HER2 gene status. 201 breast carcinoma were reviewed for HER2 gene amplification and chromosome 17 status. FISH analysis was performed by using double probes (LSI/CEP). Absolute gene copy number was also scored per each probe. HER2 FISH test was repeated on serial tissue sections, ranging in thickness from 3 to 20 µm. Ratio was scored and subsequently corrected by monosomy after gold control test using the aCGH method to overcome false interpretation due to artefactual nuclear truncation. HER2 immunotests was performed on all cases. 26/201 cases were amplified (13%). Single signals per CEP17 were revealed in 7/201 (3.5%) cases. Five out of 7 cases appeared monosomic with aCGH (overall, 5/201, 2.5%) and evidenced single signals in >60% of nuclei after second-look on FISH when matching both techniques. Among 5, one case showed amplification with a pattern 7/1 (HER2/CEP17>2) of copies (3+ at immunotest); three cases revealed single signals per both probes (LSI/CEP=1) and one case revealed a 3:1 ratio; all last 4 cases showed 0/1+ immunoscore. We concluded that: 1) monosomy of chromosome 17 may be observed in 2.5% of breast carcinoma; 2) monosomy of chromosome 17 due to biological reasons rather than nuclear truncation was observed when using the cut-off of 60% of nuclei harboring single signals; 3) the skewing of the ratio due to single centromeric 17 probe may lead to false positive evaluation; 4) breast carcinomas showing a 3:1 ratio (HER2/CEP17) usually show negative 0/1+ immunoscore and <6 gene copy number at FISH.
ISSN: 2156-6976
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