Recherche de la mutation T790Â MÂ : savoir persévérer

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 T790 M resistant mutation. The prescription of osimertinib (TKI-EGFR3G) in second line is dependent on identification of the T790 M mutation. We report 7 cases in which the identification of the T790 M 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 T790 M mutation and we encourage persevering in this search when no alternative mechanism of resistance has been identified.