Intratumoral heterogeneity of EGFR-activating mutations in advanced NSCLC patients at the single-cell level.

Background: Intratumoral epidermal growth factor receptor (EGFR) mutational heterogeneity is yet controversial in non-small cell lung cancer (NSCLC) patients. Single-cell analysis provides the genetic profile of single cancer cells and an in-depth understanding of the heterogeneity of a tumor.

Methods: Firstly, single H1975 cells harboring the EGFR L858R mutation were submitted to flow cytometry isolation, nested polymerase chain reaction (nested-PCR) amplification, and direct DNA sequencing to assess the feasibility of single-cell direct DNA sequencing. Then, the single cells of patients with lung adenocarcinoma receiving gefitinib were captured by laser capture microdissection and analyzed by the above methods to identify the intratumoral heterogeneity of the EGFR L858R mutant. Three patients with progression-free survival (PFS) > 14 months were categorized as the long PFS group, and 3 patients with PFS < 6 months as the short PFS group. The correlation between the abundance of EGFR L858R mutant and PFS was analyzed.

Results: 104 single H1975 cells were isolated. 100/104 were amplified by nested-PCR and confirmed by direct sequencing. We captured 135 tumor cells from the tissues of six patients. 120 single tumor cells were successfully amplified and sequenced. The rate of EGFR exon 21 mutation was only 77.5% (93/120). Furthermore, the rate of mutation in exon 21 of EGFR was significantly higher in the long PFS group than in the short PFS group (86.4 ± 4.9% vs. 68.9 ± 2.8%, P = 0.021).

Conclusion: Our study suggested the intratumoral heterogeneity of EGFR-activating mutations in lung adenocarcinoma confirmed on the single-cell level, which might be associated with EGFR-TKIs response in lung adenocarcinoma patients harboring the EGFR L858R mutation.