Abstract 5244: Next-generation sequence analysis of cell-free DNA in patients with chemotherapy-refractory advanced pancreatic adenocarcinoma (PDAC) treated with selumetinib (AZD6244) and erlotinib
Authors: Ko Andrew H. , Bekaii-Saab Tanios , Courtin Ryan , Mirzoeva Olga K. , Ziyeh Sharvina , Kelley Robin K. , Ditto Elizabeth , Ong Anna , Linetskaya Regina , Tempero Margaret , Venook Alan P. , Talasaz Amirali , Korn Wolfgang Michael 
Published: August 2015

Abstract
Background: Monitoring molecular events in response to treatment with targeted agents is particularly challenging in pancreatic cancer due to its poor accessibility for biopsies and high stroma content. Recent advances in digital sequencing of rare DNA species allows for detection of circulating tumor-derived free DNA (ctDNA) in plasma of patients with cancer. Here, we explored the potential of gaining information on the genomic composition of pancreatic cancers in patients treated with a combination of the MEK inhibitor selumetinib (AZD6244) and the EGFR kinase inhibitor, erlotinib.
Methods: 46 patients were enrolled into this study at two study centers. Treatment consisted of erlotinib 100 mg + AZD6244 100 mg daily in 3-week cycles, with tumor evaluation by CT scan every 2 cycles. Primary objective was overall survival (OS). Correlative endpoints included assessment of expression of EMT-related proteins, and next-generation sequencing analysis of ctDNA. Plasma “on treatment” samples were uniformly obtained at the 6 week time point.
Results: Our preclinical studies had demonstrated that inhibition of MEK leads to enhanced signaling through EGFR with hyperactivation of a parallel RAS effector pathway (PI3K), supporting a therapeutic strategy of combined target inhibition in PDAC to overcome this negative feedback loop. Disease control rate was 58% (0 PR; 19 with stable disease (SD) &gt; 6 weeks, 12 with SD &gt; 12 weeks, including 12 (26%) minor responses). 13/34 patients (38%) demonstrated CA19-9 decline &gt; 50%. Assessment of E-cadherin expression in pre-treatment FFPE biopsy material revealed that high expression of the protein was associated with greater likelihood of CA19-9 decline. Paired pre- and on-treatment plasma samples were available for digital sequencing of ctDNA using the Guardant360 assay for 32 patients. Sequence variants likely originating from the tumor (based on allele frequency and absence in the above-mentioned germ-line variants) were found in 27 (84%) pre-treatment and 25 (78%) on-treatment samples. Most frequently mutated gene in pre-therapeutic plasma samples, in which circulating tumor fraction is &gt; 0.4%, was KRAS (85%), followed by TP53 (60%), ATM (30%), and CDKN2A (15%). Relative change in allele frequency for those alleles that were present in pre- and on-treatment biopsies were positively correlated with differences in RECIST measurements.
Conclusions: In summary, dual targeting of EGFR/MEK signaling shows antitumor activity in PDAC in a subset of patients, in particular those with high levels of E-cadherin expression, which is in agreement with our preclinical findings. Digital sequencing of ctDNA provides information about genomic alterations in the majority of patients and holds the potential of providing early information on response to therapy. Supported by CTEP and NIH R21 CA149939.
Citation Format: Andrew H. Ko, Tanios Bekaii-Saab, Ryan Courtin, Olga K. Mirzoeva, Sharvina Ziyeh, Robin K. Kelley, Elizabeth Ditto, Anna Ong, Regina Linetskaya, Margaret Tempero, Alan P. Venook, Amirali Talasaz, Wolfgang Michael Korn. Next-generation sequence analysis of cell-free DNA in patients with chemotherapy-refractory advanced pancreatic adenocarcinoma (PDAC) treated with selumetinib (AZD6244) and erlotinib. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5244. doi:10.1158/1538-7445.AM2015-5244