|LETTER TO EDITOR
|Year : 2020 | Volume
| Issue : 1 | Page : 144-145
Authors' reply to Chadha et al., Sambath et al., and Sharma et al.
Avinash Pandey1, Sarjana Dutt2, Anjana Singh1, Amit Kumar1, Shivkant Singh1
1 Department of Medical Oncology, Indira Gandhi Institute of Medical Sciences, Patna, Bihar, India
2 Molecular Biology and Cytogenetics, Oncquest Laboratory, New Delhi, India
|Date of Submission||14-Jan-2020|
|Date of Decision||16-Jan-2020|
|Date of Acceptance||21-Jan-2020|
|Date of Web Publication||24-Feb-2020|
Department of Medical Oncology, Indira Gandhi Institute of Medical Sciences, Patna, Bihar
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Pandey A, Dutt S, Singh A, Kumar A, Singh S. Authors' reply to Chadha et al., Sambath et al., and Sharma et al. Cancer Res Stat Treat 2020;3:144-5
|How to cite this URL:|
Pandey A, Dutt S, Singh A, Kumar A, Singh S. Authors' reply to Chadha et al., Sambath et al., and Sharma et al. Cancer Res Stat Treat [serial online] 2020 [cited 2020 Apr 3];3:144-5. Available from: http://www.crstonline.com/text.asp?2020/3/1/144/279103
Chadha et al. have cautioned about the importance of the pre-analytical factors – immediate separation and storage of plasma or use of special tubes to stabilize nucleated cells to minimize the contamination of genomic DNA. In our study, we have used PAXgene Blood cfDNA Tube (BD) for the collection and transportation of the samples. The stabilization reagent in the PAXgene Blood cfDNA Tube prevents blood coagulation, lysis of red blood cells, and apoptosis of white blood cells. The stabilization reagent in the tube is free of cross-linking or cross-linker releasing substances and hence does not chemically modify cfDNA. In a study published in 2017, Warton et al. evaluated the PAXgene Blood cfDNA System for the use of cell-free circulating DNA studies in plasma. They found that the total yield of cfDNA remained stabilized in the PAXgene tubes even when the samples were stored for 7 days at room temperature.
For the collection of plasma, we follow the double centrifugation protocol which increases the yield of high-quality plasma. This approach of pre-analytical and processing protocol in our laboratory has resulted in a significantly low percentage (~3%) of unsatisfactory results for circulating cell free DNA for digital droplet Polymerase Chain Reaction (ddPCR) for EGFR testing (unpublished data).
We concur that in the EGFR mutation-negative liquid biopsy cohort, tumor biopsy should be considered to confirm mutation status, as the sensitivity of liquid biopsy is 70%. Our study only had patients for whom tissue-based biopsy was not feasible upfront. At data lock time point with a median follow-up of 14 months, in the EGFR-negative cohort, 3/5 patients who had refused biopsy, 4/5 in whom biopsy was not feasible, and 4/5 in whom tissue was inadequate had succumbed due to early disease progression. Hence, we could not perform invasive tissue biopsies at later time points or at progression for the above cohort.
Sambath et al. have pointed out correctly that our study was retrospective and had exclusively nonsmokers, as we wanted to enrich the yield of mutation-positive liquid biopsies. Among the nonsmoking, biopsy-ineligible, female-preponderant population, our liquid biopsy EGFR mutation positivity was 39%. This may vary if tested prospectively in unselected wider population of metastatic non-small cell lung cancer patients including smokers. We did not pursue patients who progressed on the first-line therapy in either EGFR mutation-negative or mutation-positive cohort, with invasive tissue biopsy or liquid biopsy to detect emerging drug-sensitive targetable mutations, including T790M.
Sharma et al. have commented that the ideal source of liquid biopsy (ctDNA, CTCs, exosomes, platelets, and microRNA) has not been ascertained yet. We would like to point out that laboratory science and clinical pathology are in a state of dynamic growth, and it is true that many different analytes from the plasma samples are being evaluated as a source of tumor DNA. However, to date, ctDNA is considered to be the best analyte as liquid biopsy for EGFR testing. Studies have shown that ctDNA is a feasible sample type for real-world EGFR mutation testing if robust and sensitive DNA extraction and mutation analysis methodologies are employed.,
They have further pointed out that there is still a lack of clarity about the method to be used to detect biomarkers in the liquid biopsy [digital droplet Polymerase Chain Reaction (ddPCR), Next Generation Sequencing (NGS) and Reverse Transcriptase Polymerase Chain Reaction (RTPCR)]. Multiple elegant studies have been published that the analytical performance of the ddPCR, with a detection limit of 0.05%–0.1%, is in concordance with deep-sequencing NGS and RT PCR and has high specificity and sensitivity for detecting EGFR mutations.,
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Conflicts of interest
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