Establishment of a Flow Cytometry Protocol for Binarily Detecting Circulating Tumor Cells with EGFR Mutation

Patients with EGFR-mutated non-small cell lung cancer (NSCLC) respond well to EGFR tyrosine kinase inhibitors (TKIs), but current EGFR mutation profiling relies on invasive tumor biopsies. Developing less invasive approaches, particularly proteomic evaluation of circulating tumor cells (CTCs) for EGFR mutation profiling, remains crucial.

A flow cytometry method for detecting EGFR^L858R-bearing CTCs was established by spiking NCI-H1975 cells into blood from cancer-naive donors. The method was then applied to blood samples from 21 NSCLC patients and 10 cancer-naive donors.

The gating strategy was defined by CD45^-CK-7/8⁺CK-14/15/16/19^-EpCAM⁺vimentin⁺EGFR^L858R, with a cut-off value of 5 cells/mL. The method yielded positive results in all seven patients with the EGFR^L858R mutation and negative results in all ten cancer-naive donors. Compared to the PCR-based reference method, the approach showed 100% positive and 71% negative agreement. Crucially, our in-house method detected EGFR^L858R-bearing CTCs in three patients initially identified as EGFR wild-type and one patient with a different EGFR mutation. The remaining samples were concordant with PCR. Notably, two patients with these discordant results received EGFR-TKIs and experienced partial responses.

This study introduces a feasible, less invasive proteomic approach for binarily detecting EGFR mutations in CTCs, offering a novel means for patient identification.