Background:

EGFR mutation testing is required to identify patients who may respond to TKI therapy. However, tumor biopsies from NSCLC patients can pose challenges for molecular analyses due to inadequate sample material, the inability to biopsy patients due to poor health status or inaccessible lesions, and tumor heterogeneity. We examined the detection of EGFR mutations in circulating cell-free DNA (cfDNA) from plasma and the concordance of EGFR mutation status with contemporaneously matched tumor tissue in TIGER-X, a Phase 1/2 clinical study of rociletinib (CO-1686) in previously treated advanced NSCLC patients harboring EGFR mutations in their tumors. Rociletinib is an oral, potent, small-molecule irreversible tyrosine kinase inhibitor that selectively targets mutant forms of EGFR, including T790M, L858R and Del(19), while sparing wild-type EGFR.

Methods:

Pretreatment matched tumor tissue and plasma from 139 Stage IIIB/IV NSCLC patients enrolled in TIGER-X were evaluated for EGFR status. Tumor tissue was processed as FFPE and tested by allele-specific PCR. Plasma was tested as a two mL aliquot using BEAMing, a quantitative and sensitive detection technology based on digital PCR.

Results:

Using tissue as the reference, the positive percent agreement between tumor and BEAMing plasma test results was 86% (102/119) for activating mutations and 77% (78/101) for T790M. Four plasma samples of the 23 tumor T790M+/plasma T790M- cases were also tested by three independent plasma testing platforms with claimed analytical sensitivities of <10 molecules/mL. All four plasma cases were T790M- by each test method. Of the 139 patients evaluated, there were 14 cases that were tumor T790M-/plasma T790M+. Seven of these were retested by a second plasma test platform, and five were confirmed as positive. The remaining two were near the limit of detection by BEAMing. Nine tumor samples from the plasma T790M+ cases could not be analyzed due to insufficient material. Clinical characteristics positively associated with the ability to identify EGFR mutations in plasma included M1b disease and higher tumor burden. Serial plasma assessments were performed on a subset of patients. A drop in plasma mutant EGFR levels to ≤10 molecules/mL was seen by Day 21 of treatment in 7 of 8 patients assessed who eventually experienced a PR. Re-emergence of the EGFR activating mutation in plasma, consistent with development of acquired resistance to rociletinib, was observed as early as 12 weeks prior to clinical progression by RECIST.

Conclusions:

The BEAMing plasma test identified EGFR mutations detected in tumor with high sensitivity. In addition, plasma testing identified T790M+ patients that were determined T790M- by the tumor test, which may be in part explained by tumor heterogeneity and/or inadequate biopsy. These findings demonstrate that BEAMing can be a useful tool for the non-invasive assessment of EGFR mutations in NSCLC.

Citation Format: Jonathan W. Goldman, Chris Karlovich, Elaina Mann, Lindsey Rolfe, Shannon Matheny, Darrin Despain, Philipp Angenendt, Claudia Stamm, Heather A. Wakelee, Jean-Charles Soria, Benjamin Solomon, D. R. Camidge, Rafal Dziadziuszko, Leora Horn, Shirish Gadgeel, Mitch Raponi, Andrew R. Allen, Lecia V. Sequist. Pretreatment and serial plasma assessments of EGFR mutations in NSCLC patients treated with rociletinib (CO-1686). [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 927. doi:10.1158/1538-7445.AM2015-927