While we cannot confirm that EGFR L858R and Y891D occur in cis in our patient’s tumor (since sequencing reads do not span both alterations), our findings from cell viability assays that L858R + Y891D in cis promotes resistance to early generation EGFR inhibitors is consistent with prior reports of clinical resistance to first generation inhibitors caused by Y891D21,22. The gene discussed is EGFR; the disease is neoplasm.