This study aims to describe EGFR mutation status detected in plasma samples and analyze some related factors in non-small cell lung cancer patients after treatment with the generation I and II Tyrosine Kinase inhibitors at Bach Mai Hospital. Patients and methods: A retrospective descriptive study on 75 patients with non-small cell lung cancer tested for EGFR mutations in plasma after treatment with 1st or 2nd EGFR-TKIs in 2019-2020. Results: EGFR mutations were detected in 97.3% plasma samples; the T790M mutation accounted for 37.3% and is accompanied by a sensitive mutation TKI; The T790M mutations ratio after treatment was higher than before treatment with TKIs (p < 0.001); the median total duration of EGFR-TKI treatment was significantly longer in patients with T790M mutation than in those without (16.8 months vs 12.5 months, p = 0.005); the T790M mutation ratio was higher in patients with a deletion on exon 19 than in L858R mutation on exon 21 (p=0.028), in Erlotinib treatment group higher than in Gefitinib and Afatinib treatment group (51.4% vs. with 20.0% and 33.3%, p=0.039). Conclusions: EGFR mutation plasma test helps to monitor disease progression and detect resistance mutations T790M in NSCLC patients after TKI generation I and II.
 Keywords: non-small cell lung cancer, EGFR mutations, T790M mutations, TKIs..
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