For instance, one patient who was treated with the EGFR tyrosine kinase inhibitor erlotinib showed emergence of blood-derived EGFR amplification after disease progression (Fig 4), consistent with a previous report demonstrating tumor evolution with EGFR amplification as a potential resistance mechanism to EGFR tyrosine kinase inhibitor administration.52 Perhaps relevant in this regard, all of our responders had an EGFR antibody included in their regimen. Here, EGFR is linked to neoplasm.