An additional consideration from the above-mentioned results is that when the occurrence of T790M in patients progressing on early generation EGFR-TKIs is determined only by mutation analysis of plasma cfDNA before allocation to osimertinib treatment, one may risk missing a possible concomitant transformation to SCLC or SqCC, as well as cases with EMT or AXL overexpression, thereby neglecting these causes of primary resistance to osimertinib [72,242]. This evidence concerns the gene EGFR and small cell lung carcinoma.