A 60-year-old woman, never smoker, presents with shortness of breath and is diagnosed with metastatic lung adenocarcinoma. Tumor tissue from her initial diagnostic lung biopsy is sent for molecular testing and is returned as “insufficient tumor tissue for analysis.” Blood is sent for circulating tumor DNA (ctDNA) testing using the cobas v2 EGFR assay, and the results are positive for an
exon 19 deletion. She is started on first-line therapy with an epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor. The detection of a driver mutation with ctDNA testing in this setting can be interpreted as a true-positive result and can be acted upon (Figure A).