EGFR and neoplasm: This is suggested by our representative patient who was treated with pembrolizumab, had a mixed response, and then received erlotinib and cetuximab (in addition to ongoing pembrolizumab) and showed reduction in EGFR cfDNA copy number as well as regression of tumor foci and improvement in pain and performance status (Fig 4, patient 26; Figs 5A and 5B).39,40 Additional investigation is required to understand the complex interplay of response and resistance associated with EGFR amplifications, EGFR-targeting pharmaceuticals, and checkpoint blockade.