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Laetitia Borsu

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    P1.01 - Advanced NSCLC (Not CME Accredited Session) (ID 933)

    • Event: WCLC 2018
    • Type: Poster Viewing in the Exhibit Hall
    • Track:
    • Presentations: 1
    • Moderators:
    • Coordinates: 9/24/2018, 16:45 - 18:00, Exhibit Hall
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      P1.01-75 - Utility of cfDNA Testing for Acquired Resistance: The Memorial Sloan Kettering Experience with Plasma EGFR T790M Clinical Testing. (ID 12514)

      16:45 - 18:00  |  Author(s): Laetitia Borsu

      • Abstract
      • Slides


      Liquid biopsy for circulating tumor DNA (ctDNA) has been increasingly adopted for the detection of oncogenic drivers and drug resistance mechanisms. Practice guidelines for liquid biopsy are lacking and biologic factors influencing ctDNA detection and shedding are poorly understood. We evaluated factors influencing ctDNA detection, using EGFR-T790M as a case-study, in patients with acquired resistance to first/second-generation EGFR tyrosine kinase inhibitors (EGFR-TKI).

      a9ded1e5ce5d75814730bb4caaf49419 Method

      This single-center study included metastatic sensitizing EGFR-mutant lung cancer patients (exon 19 deletions, L858R, G719) who underwent plasma EGFR-T790M testing after acquired resistance to erlotinib, gefitinib, or afatinib between January 2016 and August 2017. Plasma T790M was performed by digital PCR. Variant allele fraction (VAF) was calculated as mutant/(wildtype+mutant) allele. Concordance between plasma and tissue testing was examined if tissue analysis (MSK-IMPACT and/or targeted PCR) occurred within 90 days of blood draw. Turnaround time (TAT) was measured from date of blood draw and/or biopsy to result. ctDNA results were correlated with metastatic site and the number of organs involved.

      4c3880bb027f159e801041b1021e88e8 Result

      177 patients underwent plasma T790M testing; 65% female, 47% current/former smokers. Plasma T790M was positive in 32% (56/177) of patients, tissue testing was T790M-positive in 46% (45/97), and overall T790M-positivity by either platform was 49% (86/177). The median TAT was shorter for plasma T790M compared to tissue PCR (9 vs 15 days, p<0.0001), and led to osimertinib use in 84% (47/56) of positive patients. Concordance between plasma and tissue T790M was 80% (32/40). 15 patients with positive plasma had matched tissue, 87% (13/15) were concordant on tissue. 76% (19/25) of the patients that were T790M-negative on plasma also tested negative on tissue. Median plasma T790M-VAF was 0.98% (range 0.1–49.5%), lower than tissue T790M-VAF (12.8%, range 2.58–27.8, p<0.0001). Plasma T790M-VAF did not correlate with time on osimertinib (p=0.72). Plasma T790M status correlated with a higher number of metastatic sites (4 vs 3, p<0.0001). Plasma T790M detection by organ sites were: pleura (58% with metastases vs 34% without metastases, p=0.14), bone (80% vs 21%, p=0.0002), hepatic (61% vs 41%, p=0.28), nodal (61% vs 33%, p=0.07), adrenal (64% vs 44%, p=0.60), brain (71% vs 38%, p=0.08), and bone/hepatic concurrently (94% vs 98%, p=0.04).

      8eea62084ca7e541d918e823422bd82e Conclusion

      Using plasma T790M as an archetypal example, cfDNA testing showed concordance and a shorter turnaround compared to tissue testing. cfDNA was more likely to result positive in patients with more metastatic sites, or osseous and hepatic metastases possibly driven by increased ctDNA shedding.


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