Molecular Analysis of Plasma From Patients With ROS1-Positive NSCLC

Abstract

Introduction: Circulating tumor DNA analysis is an emerging genotyping strategy that can identify tumorspecific genetic alterations in plasma including mutations and rearrangements. Detection of ROS1 fusions in plasma requires genotyping approaches that cover multiple breakpoints and target a variety of fusion partners. Compared to other molecular subsets of NSCLC, experience with detecting ROS1 genetic alterations in plasma is limited. Methods: To describe the spectrum of ROS1 fusions in NSCLC and determine sensitivity for detecting ROS1 fusions in plasma, we queried the Guardant Health plasma dataset and an institutional tissue database and compared plasma findings to tissue results. In addition, we used the Guar-dant360 NGS assay to detect potential genetic mediators of resistance in plasma from patients with ROS1-positive NSCLC who were relapsing on crizotinib. Results: We detected seven distinct fusion partners in plasma, most of which (n ¼ 6 of 7) were also represented in the tissue dataset. Fusions pairing CD74 with ROS1 predominated in both cohorts (plasma: n ¼ 35 of 56, 63%; tissue: n ¼ 26 of 52, 50%). There was 100% concordance between the specific tissue-and plasmadetected ROS1 fusion for seven patients genotyped with both methods. Sensitivity for detecting ROS1 fusions in plasma at relapse on ROS1-directed therapy was 50%. Six (33%) of 18 post-crizotinib plasma specimens harbored ROS1 kinase domain mutations, five of which were ROS1 G2032R. Two (11%) post-crizotinib plasma specimens had genetic alterations (n ¼ 1 each BRAF V600E and PIK3CA E545K) potentially associated with ROS1independent signaling. Conclusions: Plasma genotyping captures the spectrum of ROS1 fusions observed in tissue. Plasma genotyping is a promising approach to detecting mutations that drive resistance to ROS1-directed therapies.

Clinical relevance of blood-based ctDNA analysis: mutation detection and beyond

“…69,70 These structural genomic abnormalities have the potential to be detected via NGS techniques with the additional benefit of detecting a large number of gene fusions with known and unknown partner genes, compared with previous targeted PCR assays. Indeed, data obtained over the past 1-2 years have shown that plasma genotyping using hybrid-capture NGS technology can reliably detect ALK or ROS fusions in NSCLC patients, 71,72 although these results need to be confirmed in larger patient cohorts.…”

Focus on ROS1-Positive Non-Small Cell Lung Cancer (NSCLC): Crizotinib, Resistance Mechanisms and the Newer Generation of Targeted Therapies

“…Consequently, it might be thought that the addition of a KIT inhibitor such as ponatinib might be beneficial in such cases. Lastly, upregulation of MAPK signalling plus the amplification of TP53 and HER2 have been reported in crizotinib-resistant cells and might play a key role in bypass mechanisms [45,80].…”

“…Additionally, L2155S is thought to confer crizotinib resistance via protein malfunction, whereas the S1986F/Y substitution within the kinase domain leads to an obstruction of the key site for activation, thereby increasing kinase activity [79]. Furthermore, the activation of bypass signalling as a method of crizotinib resistance in ROS1 cancer cells has been described in various studies and identified in approximately 45% of crizotinib-resistant ROS1-rearranged NSCLC malignancies (Figure 1) [80,81]. The activation of the EGFR pathway has been shown to confer crizotinib resistance by reducing the dependence on ROS1 activity and increasing dependence on EGFR activity [79,82,83].…”

Implementing ctDNA Analysis in the Clinic: Challenges and Opportunities in Non-Small Cell Lung Cancer

“…Likewise, other oncogene-addicted NSCLC patients progressing under ALK or ROS1 tyrosine kinase inhibitors were shown to benefit from the optimization of subsequent treatment strategies based on ctDNA characterization [42,65,69].…”