HER2, chromosome 17 polysomy and DNA ploidy status in breast cancer; a translational study

Altuna Halilovic,Marian J P L Stevens-Kroef,Oliver B A Boelens,Carlijn Van De Water,Jolien Tol,Dagmar I Verweij,Irene Otte-Höller,Margrethe S Schlooz-Vries,Jeroen R Dijkstra,Bastiaan B J Tops,Janet Elsink,Iris D Nagtegaal,Annet Simons,Jeroen A W M Van Der Laak,Susan Vermeulen,Patricia H J Van Cleef,Peter Bult,Paul N Span

doi:10.1038/s41598-019-48212-2

Abstract

Breast cancer treatment depends on human epidermal growth factor receptor-2 (HER2) status, which is often determined using dual probe fluorescence in situ hybridisation (FISH). Hereby, also loss and gain of the centromere of chromosome 17 (CEP17) can be observed (HER2 is located on chromosome 17). CEP17 gain can lead to difficulty in interpretation of HER2 status, since this might represent true polysomy. With this study we investigated whether isolated polysomy is present and how this effects HER2 status in six breast cancer cell lines and 97 breast cancer cases, using HER2 FISH and immunohistochemistry, DNA ploidy assessment and multiplex ligation dependent probe amplification. We observed no isolated polysomy of chromosome 17 in any cell line. However, FISH analysis did show CEP17 gain in five of six cell lines, which reflected gains of the whole chromosome in metaphase spreads and aneuploidy with gain of multiple chromosomes in all these cases. In patients’ samples, gain of CEP17 indeed correlated with aneuploidy of the tumour (91.1%; p < 0.001). Our results indicate that CEP17 gain is not due to isolated polysomy, but rather due to widespread aneuploidy with gain of multiple chromosomes. As aneuploidy is associated with poor clinical outcome, irrespective of tumour grade, this could improve future therapeutic decision making.

Highlights

Human epidermal growth factor receptor-2 (HER2) status assessment is of pivotal importance for targeted therapy for human epidermal growth factor receptor-2 (HER2) positive primary[1,2,3,4] and metastatic[5,6,7] breast cancer
Copy number gain of chromosome 17 correlated with a tetraploid or aneuploid pattern with gains in the DNA ploidy assessment in five of six cell lines. These data show that copy number gain of CEP17 is not due to isolated chromosome 17 polysomy, but is a result of aneuploidy with gain of multiple chromosomes
CEP17 copy number gain can lead to difficulties in the interpretation of HER2 status, but it is still disputed whether this represents true chromosome 17 polysomy

Summary

Introduction

Human epidermal growth factor receptor-2 (HER2) status assessment is of pivotal importance for targeted therapy for HER2 positive primary[1,2,3,4] and metastatic[5,6,7] breast cancer. Dual probe ISH includes a probe for the ERBB2(HER2) gene and a probe for the centromere of chromosome 17 (CEP17), so copy number changes can be found for both locations. Gain of CEP17, which is commonly interpreted as chromosome 17 polysomy, is said to be present in up to 68% of breast carcinomas according to various studies[10,11]. In addition to losses and gains of HER2 and CEP17, copy number alterations of other parts of chromosome 17 occur. The clinical relevance of copy number alterations in these genes is not yet clear. With the present study we aimed to investigate the presence or absence of chromosome 17 polysomy in relation to CEP17 gains and with respect to HER2 status assessment, by combining in vitro assays with clinical validation cases

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