EGFR and non-small cell lung carcinoma: A patient with NSCLC and an EGFR exon 19 deletion was also found to have a simultaneous EGFR T790M mutation on a tumor biopsy obtained after progression while taking the EGFR tyrosine kinase inhibitor erlotinib; however, unlike with the EGFR exon 19 deletion (12.86%), EGFR T790M was no longer present in cfDNA obtained 10 months after having been taken off erlotinib.