Circulating Tumor DNA as a Liquid Biopsy: Current Clinical Applicati…ture Directions: Page 2 of 3 | Cancer Network | The Oncology Journal 11/19/17, 10(40 PM Circulating Tumor DNA as a Liquid Biopsy: Current Clinical Applications and Future Directions: Page 2 of 3 By Kimberly M. Komatsubara, MD and Adrian G. Sacher, MD, MMSc Tuesday, August 15, 2017 Issue: Volume: 31 8 Oncology Journal, Cancer and Genetics Abstract / Synopsis: Tumor genomic sequencing has become part of routine oncology practice in many tumor types, in order to identify potentially targetable mutations and to personalize cancer care. Plasma genotyping via circulating tumor DNA analysis is a noninvasive and rapid alternative method of detecting and monitoring genomic alterations throughout the course of disease. Multiple assays have been developed to date, each with different test characteristics and degrees of clinical validation. Here we review the clinical data supporting these different plasma genotyping methodologies, and present a practical approach to the interpretation of the results of these tests. While the clinical application of plasma genotyping has been most extensively validated in the metastatic setting—for the detection of targetable alterations at the time of initial diagnosis or disease progression— this technology holds significant promise across many tumor types and stages of disease. We will also review emerging applications of plasma genotyping that are currently under clinical investigation. http://www.cancernetwork.com/oncology-journal/circulating-tumor-dna-li…id-biopsy-current-clinical-applications-and-future-directions/page/0/1 Page 1 of 4 Circulating Tumor DNA as a Liquid Biopsy: Current Clinical Applicati…ture Directions: Page 2 of 3 | Cancer Network | The Oncology Journal 11/19/17, 10(40 PM Guide to Interpretation of Plasma Genotyping Results Oncology (Williston Park). 31(8):618– With a multitude of commercial assays now available, plasma 627. genotyping is quickly emerging as a routine tool in the armamentarium available for the diagnosis and management of cancer. The clinical utility of plasma genotyping for directing patient care has been most extensively studied at the times of initial diagnosis and disease progression in advanced lung cancer, where molecular testing results directly impact treatment decision making. While tumor tissue genotyping is considered the standard choice for detection of potentially targetable alterations, plasma Table 1. Comparison of Selected ctDNA genotyping may have a role, particularly in settings where either a Assays for Detection of EGFR Mutations tissue biopsy is technically infeasible or tissue is inadequate to perform routine genotyping. Plasma genotyping at initial diagnosis Table 2. Interpretation of ctDNA Testing Careful consideration of the biology underlying ctDNA shed and an Results understanding of the characteristics of the particular assay being used are required to accurately interpret ctDNA test results. As discussed in the aforementioned studies, validated ctDNA assays are characterized by exquisitely high specificity and positive predictive values. As a result, a driver mutation detected by plasma genotyping can be interpreted as a true-positive result. The ability to detect a driver mutation also implies that a tumor is shedding ctDNA at a detectable level. Thus, any negative result in this setting can also be interpreted as a true negative (Table 2). For example, the absence of an EGFR mutation on plasma genotyping, but detection of a KRAS ctDNA mutation, can be interpreted as a true- negative result and a true-positive result, respectively. Interpretation is more complex in the setting where no genomic Figure. Circulating Tumor DNA as a Liquid Biopsy alterations are detected. In such a case, either the tumor does not possess any of the mutations of interest, or the tumor is not shedding any ctDNA—meaning that the result might be a false http://www.cancernetwork.com/oncology-journal/circulating-tumor-dna-li…id-biopsy-current-clinical-applications-and-future-directions/page/0/1 Page 2 of 4 Circulating Tumor DNA as a Liquid Biopsy: Current Clinical Applicati…ture Directions: Page 2 of 3 | Cancer Network | The Oncology Journal 11/19/17, 10(40 PM negative. Furthermore, while the majority of plasma genotyping assays have near-perfect specificity, sensitivity generally ranges from 70% to 80%, resulting in false-negative tests due to inherent analytic test factors. Thus, a tumor biopsy for confirmatory genotyping should be considered when plasma genotyping results are entirely negative (see Table 2). Figure A Plasma genotyping for resistance mutations The ability to detect resistance mutations at disease progression is another property of noninvasive testing with plasma genotyping that may be particularly valuable clinically. The detection of EGFR T790M mutations by ctDNA analysis is a key example of this clinical application. Multiple studies in this particular setting have reported lower specificities for the detection of EGFR T790M when Figure B plasma genotyping has been compared with tissue genotyping. Thress et al reported sensitivities of 73% and 81% and specificities of 67% and 58% when using the cobas and BEAMing platforms, respectively, for the detection of EGFR T790M. In their analysis they concluded that many of the “false-positive” results were more likely explained by tumor heterogeneity of resistance mutations, rather than being due to a lack of specificity of the assay.[27] Interestingly, subsequent studies have demonstrated that patients treated with osimertinib based on a positive plasma test for the EGFR T790M mutation have outcomes similar to those of patients who are treated based on tissue genotyping results. [20] The recent confirmatory AURA3 study, which randomized patients with T790M-positive NSCLC who had progressed following treatment with at least one EGFR kinase inhibitor to either osimertinib or platinum-based chemotherapy, demonstrated similar outcomes for patients who were T790M-positive by ctDNA testing and those positive by tumor testing, supporting the feasibility of using plasma genotyping in this clinical setting.[28] Thus, with regard to resistance mutation detection, plasma genotyping may be useful to confirm the presence of a targetable resistance mutation such as EGFR T790M. Because the sensitivity of plasma genotyping assays is not perfect, however, a negative ctDNA test should still be followed by a reflex tumor biopsy when feasible, since the latter may identify alternate mechanisms of resistance, such as transformation of disease or complex alterations, which are not as easily identified by plasma genotyping. http://www.cancernetwork.com/oncology-journal/circulating-tumor-dna-li…id-biopsy-current-clinical-applications-and-future-directions/page/0/1 Page 3 of 4 Circulating Tumor DNA as a Liquid Biopsy: Current Clinical Applicati…ture Directions: Page 2 of 3 | Cancer Network | The Oncology Journal 11/19/17, 10(40 PM « first ‹ previous 1 2 3 next › last » © 2017 UBM Medica, LLC, a UBM company. All rights reserved. Reproduction in whole or in part is prohibited. Please send any technical comments or questions to our webmaster. http://www.cancernetwork.com/oncology-journal/circulating-tumor-dna-li…id-biopsy-current-clinical-applications-and-future-directions/page/0/1 Page 4 of 4 Circulating Tumor DNA as a Liquid Biopsy: Current Clinical Applications and Future Directions | Cancer Network | The Oncology Journal 12/22/17, 951 PM Circulating Tumor DNA as a Liquid Biopsy: Current Clinical Applications and Future Directions By Kimberly M. Komatsubara, MD and Adrian G. Sacher, MD, MMSc Tuesday, August 15, 2017 Issue: Volume: 31 8 Oncology Journal, Cancer and Genetics Abstract / Synopsis: Tumor genomic sequencing has become part of routine oncology practice in many tumor types, in order to identify potentially targetable mutations and to personalize cancer care. Plasma genotyping via circulating tumor DNA analysis is a noninvasive and rapid alternative method of detecting and monitoring genomic alterations throughout the course of disease. Multiple assays have been developed to date, each with different test characteristics and degrees of clinical validation. Here we review the clinical data supporting these different plasma genotyping methodologies, and present a practical approach to the interpretation of the results of these tests. While the clinical application of plasma genotyping has been most extensively validated in the metastatic setting—for the detection of targetable alterations at the time of initial diagnosis or disease progression— this technology holds significant promise across many tumor types and stages of disease. We will also review emerging applications of plasma genotyping that are currently under clinical investigation. http://www.cancernetwork.com/review-article/circulating-tumor-dna-liquid-biopsy-current-clinical-applications-and-future-directions Page 1 of 6 Circulating Tumor DNA as a Liquid Biopsy: Current Clinical Applications and Future Directions | Cancer Network | The Oncology Journal 12/22/17, 951 PM Introduction Modern targeted therapies have greatly advanced the treatment of Oncology (Williston Park). 31(8):618– many solid tumors. The rational use of these agents requires 627. optimal strategies for the rapid and accurate detection of targetable genomic alterations, both upon initial diagnosis and when acquired resistance to targeted therapies develops. While tissue genotyping has traditionally been considered the standard of