Abstract P3-06-22: Identification of ERBB2 gene variants in HER2 positive disease associated with trastuzumab response in an adjuvant trastuzumab chemotherapy trial
Authors: Gunn Shelly , Zien Alexander , Hartenfeller Markus , Diella Francesca , Brock Stephan , Stein Martin , Badbanchi Sasha , Doerks Anja , Jackson David , Asmar Lina , Wang Yunfei , Jones Steve 
Published: May 2015

Abstract
Background
Among 493 patients with early stage, lower risk (70% node negative), HER2 positive breast cancer, the 2-year DFS was 97% with adjuvant docetaxel and cyclophosphamide plus 1 year of trastuzumab (TCH) in a phase 2 study (Jones et al, Lancet Oncology 14: 1121, 2013). The objective of this work was to investigate the presence of ERBB2 specific DNA biomarkers in HER2 amplified tumors associated with relapse compared to those which did not recur during 3 years of followup.
Methods
The 26 coding exons of the ERBB2 gene were analyzed by next generation sequencing (NGS) on the HiSeq-2500 (Illumina) platform using DNA samples from the primary tumors of 13 of the 493 patients who progressed. Treatment refractory cases were analyzed in parallel with a clinically and pathologically matched group of 11 patients from the same trial with 2-year relapse free survival (RFS).
Results
ERBB2 gene variants were detected in all 11 relapse-free patients and 10/13 patients with relapse. Heterogeneity for sub-clonal ERBB2 variants at &lt;1% tumor variant frequency (TVF) was pronounced. There were 126 total distinct ERBB2 SNVs across the 24 tumors. Only 4 occurrences of SNVs known to us to be activating (G309A, D769H, D769Y, V777L, V842I, R896C, S310Y, S310F, T798M, 611M, 678M) were found: 3 times V842I and a single case with R896C. Of the investigated tumors, 5 exhibited sub-clonal hyper-mutability with &gt;30 ERBB2 SNVs. These sub-clonal ERBB2 SNVs were not detected in a comparison set of non-HER2 positive solid tumors. We did find variants that seem to be associated with later relapse, of which one is statistically significant (I655V; p=1.2%, Fisher exact test, no compensation for multiple testing), and further 5 have p&lt;10%.
Conclusions
We find no evidence for known activating HER2 mutations to confer increased (nor decreased) risk of relapse after TCH therapy (p=30.0%). Remarkably, I655V is found significantly less often in the relapse group. This variant is known to increase BC risk by activating HER2 dimerization; an effect that may be muted by trastuzumab, in contrast to some other causes of BC. Moreover, I655V mutations with high TVF (&gt;75%, hence suggesting homozygous germline presence) are exclusively found in the no-relapse group (p=3.1%). These biomarkers in combination with other molecular studies including immune function gene status may help define the subset of patients at risk for relapse during TCH therapy. The hyper-mutability genotype does not seem to correlate with later relapse, so it may be hypothized that the low TVF mutations are passengers rather than drivers. Further studies are needed to verify and precisely define the role of these ERBB2 biomarkers in HER2 positive breast cancer.
Citation Format: Shelly Gunn, Alexander Zien, Markus Hartenfeller, Francesca Diella, Stephan Brock, Martin Stein, Sasha Badbanchi, Anja Doerks, David Jackson, Lina Asmar, Yunfei Wang, Steve Jones. Identification of ERBB2 gene variants in HER2 positive disease associated with trastuzumab response in an adjuvant trastuzumab chemotherapy trial [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P3-06-22.