Abstract P5-10-18: The chromosomal genomic landscape and targetable co-amplified genes in HER2 positive breast cancer patients who relapsed on an adjuvant trastuzumab chemotherapy trial
Authors: Gunn Shelly , McCaskill Chris , Daley Linda , Puskas Agnes , Asmar Lina , Wang Yunfei , Jones Stephen 
Published: May 2015

Background

Early stage HER2 amplified breast cancer has a generally favorable prognosis with over 95% of patients showing 2-year disease free survival (DFS) when treated with adjuvant trastuzumab. However, a subset of these tumors are refractory to treatment and present a challenge for the oncologist, particularly when clinical and histologic parameters, including the patient’s nodal and hormonal status, are indicative of lower-risk HER2 positive disease. In this study we describe the genomic landscape of three clinically lower-risk patients with HER2 amplified tumors who relapsed on adjuvant docetaxel and cyclophosphamide plus 1 year of trastuzumab in a phase 2 study (Jones et al, Lancet Oncology 14: 1121, 2013). All patients’ tumors showed high-level HER2 amplification ratios by FISH (8.51-14.46) and were analyzed in parallel with a fourth clinically matched 2-year DFS patient’s tumor from the same trial with high HER2 gene amplification (FISH ratio 11.38).

Methods

Primary tumor genomic DNA analysis was performed from archival tissue by next generation sequencing (NGS) on the Illumina HiSeq 2500 platform in a CLIA certified laboratory. Tumors were screened for point mutations and copy number alterations (CNAs) by NGS using a targeted-whole exome 613 gene panel. CNAs detected by NGS were confirmed on a DNA microarray featuring high-density probe coverage of the same 613 genes on the targeted panel. CGH chromosome ratio plots were overlaid with algorithmically derived NGS copy number data to generate a map of the chromosomal genomic landscape for each patient’s tumor.

Results

High-level HER2 gene amplification status was confirmed, and co-amplified chromosome 17 genomic regions were detected in all three relapsed patients’ tumors. High-level HER2 amplification was also confirmed in the non-relapsed patient’s tumor but co-amplified regions were not detected on chromosome 17 or elsewhere in this patient’s tumor genome. Two of the relapsed ER negative tumors shared focal high-level CCNE1 gene amplifications on chromosome 19. High-level MAP3K3 gene amplification on chromosome 17 was detected in the one ER positive tumor from a relapsed patient. Focal PIK3CA gene amplifications were not identified in any of these tumors, but two tumors (one from the relapse group and one non-relapse) were positive for activating H1047R mutations.

Conclusions

Combined NGS and CGH analysis of HER2 positive early stage breast cancer can be performed in the clinical laboratory to reveal the tumor’s chromosomal genomic landscape. Combined with other test results, this tumor map can help identify patients at high-risk for relapse and reveal alternative predictive biomarkers of therapeutic response.

Citation Format: Shelly Gunn, Chris McCaskill, Linda Daley, Agnes Puskas, Lina Asmar, Yunfei Wang, Stephen Jones. The chromosomal genomic landscape and targetable co-amplified genes in HER2 positive breast cancer patients who relapsed on 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 P5-10-18.