In cases of advanced EGFR mutation-positive non-small cell lung cancer, first or second generation EGFR-tyrosine kinase inhibitors (TKI-EGFR 1G or TKI-EGFR 2G) are recommended as first line treatment. Inexorably, progressive disease occurs and, in 50-60% of the cases, is secondary to a T790M resistant mutation. The prescription of osimertinib (TKI-EGFR3G) in second line is dependent on identification of the T790M mutation. We report 7 cases in which the identification of the T790M mutation required repeated analyses of cell free DNA and/or biopsies over a period of time. In some cases, a positive result was obtained a long time after progressive disease had been diagnosed during treatment with first or second generation EGFR-TKI. We discuss here the different modalities of screening for the T790M mutation and we encourage persevering in this search when no alternative mechanism of resistance has been identified.
Keywords: Adenocarcinoma; Adénocarcinome; Cancer bronchique non à petites cellules; EGFR receptor; Mutation T790M; Non-small cell lung cancer; Osimertinib; Récepteur à l’EGF; T790M mutation.
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