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

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.

Consensus for HER2 alterations testing in non-small-cell lung cancer

“…As a dual-probe technique, FISH allows the determination of copy number changes for both the HER2 gene and the centromere of chromosome 17 (CEP17). 80 HER2 copy number gain can be defined by calculating the gene copy number or the ratio of HER2 to CEP7. In comparison with the mean HER2 copy number, the HER2 /CEP17 ratio is sometimes considered a better reflection of HER2 amplification status, as the former may be influenced by multiple factors, including abnormal chromosome copy number (aneusomy), mitotic index of the tumor, section thickness and nuclear truncation effects.…”

Validation of HER2 status in whole genome sequencing data of breast cancers with AI-driven, ploidy-corrected approach

“…This is, to the best of our knowledge, the first, the largest, and the most objective study of its kind, utilizing artificial intelligence and machine learning approaches for establishing diagnostic criteria. The optimal CAP/AAP guidelines for IHC/FISH testing took 11 years to refine, because it involved a series of consecutive evaluations and quality control rounds of diagnostic parameters which probably could have been done nowadays in an AI-based manner more robustly and quickly [6,7]. First proof-of-concept AI-based solutions for robust FISH and IHC assessment are already tested in clinical setup [26,27].…”

“…Secondly, the isolated deletion or duplication events of chromosome 17 may influence the ERBB2 transcription [4,5]. The gain of an additional copy of chromosome 17, called polysomy, is correlated with tumour ploidy and is considered its surrogate in the FISH test, but discrepancies between these parameters are in part the reason for inaccuracy in ERBB2 amplification detection [6].…”

Rapid HER2 cytologic fluorescence in situ hybridization for breast cancer using noncontact alternating current electric field mixing

“…Consequently, cytologic specimens tend to yield lower HER2/CEP17 ratios, though they are more likely to indicate the “actual” copy numbers 15 . The CEP17 gain is not due to isolated polysomy, but may instead be gains in the whole chromosome and strongly correlate with aneuploidy with gain of multiple chromosomes 30 . Although aneuploidy is associated with poor clinical outcomes, irrespective of tumor grade, problems related to aneuploidy and genomic heterogeneity are common among all high‐throughput molecular profiling techniques, including ISH.…”