My mum (73years,IVstage,small meta in lymph nodes,EGFR+,exon18,G719X), was for 21 months on 1st line Afatinib (first 40% reduction, last three months with slow progression), after that she was on pemetrexed monotherapy for 3 months with quite significant progression (30%). Since finishing on Afatinib 3 liquid biopsies for T790M have been done with no outcome - not even the original mutation showed. Tissue biopsy would be problematic.
Also one month ago, 1 lesion in brain was detected, first considered to be a brain metastasis. Now the doctors say it might rather be meningeom. Still they are not quite sure and want to observe for 1-2 months.
I think there is a really good chance my mum is T790M positive given her long time and slow progression on Afatinib.
As the best next step I see trying osimertinib (even without confirmed T790M mutation). I have already ordered it in the form of Tagrix (which we can afford) . The oncologist suggested erlotinib (which is rather unusual after 1st line afatinib and does not promise much long-term success).
Follow-ups of LUX-Lung trials show that patients who took 1st generation TKI (erlotinib) after afatinib were on this therapy for 4 months. I read results of other studies for osimertinib where patients who were T790M negative had PFS on osimertinib 3-4 months. So it seems there is nothing to lose even if it turned out my mum is T790M negative.
Can anyone give some advice/comments on this, thank you.