APE 1 is elevated in T790M‐negative EGFR ‐ TKI ‐resistant patients. APE 1 and the EMT biomarkers E‐cadherin and vimentin were assayed by IHC in the tumors of two patients receiving rebiopsy after progression following treatment with first‐generation EGFR ‐ TKI , and these markers were compared with pretreatment biopsy tissue. Both patients underwent rebiopsy at disease progression with core needle, and the tumor was determined to be T790M negative by the Cobas method