Abstract 1533: A time course study of genomic instability in breast cancer patients receiving neoadjuvant therapy with or without bevacizumab
Authors: Møller Elen K. , Nord Silje , Vollan Hans Kristian Moen , Gythfeldt Hedda von der Lippe , Edvardsen Hege , Silwal- Pandit Laxmi , Krohn Marit , Fleischer Thomas , Schlitchting Ellen , Borgen Elin , Garred Øystein , Fangberget Anne , Holmen Marit M. , Skjerven Helle , Lundgren Steinar , Wist Erik , Naume Bjørn , Børresen-Dale Anne-Lise , Lingjærde Ole Christian , Engebråten Olav , Kristensen Vessela N. 
Published: May 2015

Tumor heterogeneity is an area of intense research, revealing tumors with high complexity consisting of different subclones and infiltrating cells. Identification of subclones that are resistant to therapy may be critical to improve treatment outcome.

The NeoAva study is a randomized phase II, clinical trial of Her2 negative breast cancer patients treated in a neoadjuvant setting with chemotherapy (FEC and taxane) +/- bevacizumab. Core needle biopsies were obtained at screening and after 12 weeks, and the tumor was surgically removed after 25 weeks. DNA copy number changes in the tumors were analyzed using Affymetrix SNP Array 6.0. Allele specific copy number changes were assessed using the Allele-Specific Copy number Analysis of Tumors (ASCAT) algorithm (Van Loo, Norgard et al., PNAS 2010) and allele-specific Piecewise Constant Fitting (asPCF) algorithms (Nilsen, Liestol et al., BMC Genomics 2012). Measures of genomic instability were obtained through the complex arm-wise aberration index (CAAI) that captures local rearrangements (‘firestorms’) (Russnes, Vollan et al., Sci Transl Med 2010).

Changes in copy number aberrations between the three different time points were observed in almost all tumors. Some tumors showed a decrease in tumor percentage and aberrations after just 12 weeks of treatment, where others showed loss of aberrations only at the time of surgery (25 weeks). Most of the tumors that did retain aberrations at all time points during treatment, did not demonstrate any decrease in tumor size. Other profiles indicated subclonal reduction, where some aberrations are kept throughout treatment and others disappear. Many of the tumors shrinking in size showed fewer whole arm aberrations than before treatment, but retained their focal amplicons. Some of the tumor aberrations seem to disappear after 12 weeks, but to reappear after 25 weeks, but with the addition of novel aberration.

Complex rearrangements were identified in 67% of tumors before treatment. The most frequent ‘firestorms’ were found on 20p, 11q and 8p. Some events were persistent through therapy, but the majority changed. An association between complex tumor genomes and patients having progressive disease/non-responders were observed.

These results show the complex structure of a tumor and suggest that heterogeneity will influence the response to treatment. The subclonal patterns of tumors may be of great importance for clinical decision-making, as well as for monitoring treatment efficacy.

Citation Format: Elen K. Møller, Silje Nord, Hans Kristian Moen Vollan, Hedda von der Lippe Gythfeldt, Hege Edvardsen, Laxmi Silwal- Pandit, Marit Krohn, Thomas Fleischer, Ellen Schlitchting, Elin Borgen, Øystein Garred, Anne Fangberget, Marit M. Holmen, Helle Skjerven, Steinar Lundgren, Erik Wist, Bjørn Naume, Anne-Lise Børresen-Dale, Ole Christian Lingjærde, Olav Engebråten, Vessela N. Kristensen. A time course study of genomic instability in breast cancer patients receiving neoadjuvant therapy with or without bevacizumab. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1533. doi:10.1158/1538-7445.AM2014-1533