- Tumor samples will be obtained at baseline by a mandatory biopsy. At the time of first progression on osimertinib if a patient is eligible for surgery as a form of LAT, then a tissue sample will be obtained for genomic and proteomic studies to identify mechanisms of acquired resistance. For patients who are not eligible for LAT or a form of LAT that is not surgery (radiation, radiofrequency ablation, cryoablation), then a mandatory biopsy will be performed, if clinically safe, to obtain tissue for above studies.