According to the higher TCR diversity associated with EGFR mutations (13) and our results, we propose possible explanations for higher clonality and MOI of EGFR 19del patients: Patients with EGFR 19del may have produced more bystander T cells because of inflammation and viral infection, for example; immune studies have shown that approximately 90% of infiltrating CD8+ T cells in patients with cancer are bystander T cells, unrelated to treatment (51, 52). Here, EGFR is linked to viral infectious disease.