The increase in activating EGFR mutation in plasma is an ear
Systemic treatment of advanced non-small cell lung cancer (NSCLC) has changed dramatically since the introduction of targeted therapies. The analysis of circulating tumor DNA (ctDNA) is a valuable approach to monitor the clonal evolution of tumors during treatment with EGFR-tyrosine kinase inhibitors (TKIs) and to detect resistance mutations.

A NSCLC patient with exon 19 deletion (ex19del) of EGFR was treated with osimertinib after multiple lines of treatment and obtained a partial response that lasted over 26 months. Blood was collected at each visit and ctDNA was extracted to monitor ex19del by digital droplet PCR. Within a few weeks from the beginning of osimertinib, ex19del disappeared from plasma but appeared again and steadily increased a few months later anticipating tumor progression. Interestingly, the change in ex19del was much more pronounced than other mutations, since T790M appeared 3 months after the increase of ex19del, and C797S was detectable a few weeks before clinical disease progression. Then the patient received cytotoxic chemotherapy, which was associated with a decrease in ex19del and disappearance of T790M and C797S; however, at disease progression, all EGFR mutations increased again in plasma together with MET amplification which was detected by NGS.

Source: BMC Cancer 2019 19:410

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