De novo EGFR T790M, KRAS and PIK3CA somatic mutations in cell free DNA in non-small cell lung cancer patients and clinical characteristics.

Abstract

e20561 Background: Several mechanisms for acquired drug resistance EGFR-TKIs in NSCLC have been suggested. These include EGFR T790M mutation and mutations in KRAS, and PIK3CA. Rarely, a de novoT790M mutation has been reported. However, the clinical significance of these mutations remains controversial. Here, we used highly sensitive methods to detect T790M, KRAS and PIK3CA mutations in cell free DNA (cfDNA) and evaluate the clinical significance of those mutations. Methods: The blood samples were collected from 125 patients with NSCLC. Ion AmpliSeq Cancer Hotspot Panel (ICP) using a targeted ultra-deep sequencing (mean depth 22,868x) was performed in cfDNA, which were validated with droplet digital PCR (ddPCR). Results: ICP detected EGFR T790M mutation in 30 of 125 cfDNA (24%), KRAS mutations in 18 (14.4%) and PIK3CA in 33 (26.4%). ddPCR confirmed concordant T790M results in 22 (73.3%) and KRAS in 13 (72.2%). The 8 of 22 (36.4%) in T790M and 2 of 13 (15.4%) in KRAS had simultaneous activating EGFR mutations in cfDNA or tumor tissue. The most single KRAS mutations appeared in codon 12 (n = 7, 63.6%) (3 in G12C, 2 in G12S, 1 in G12V and 1 in G12D) with three mutations in codon 13 (27.3%) and one mutation in codon 61 (9.1%). About 20% to 50% had bone or brain metastases at diagnosis in patients with these mutations. The 5 (62.5%) (4 PR and 1 SD) of 8 patients in T790M and 8 (61.5%) (All PR) of 13 in PIK3CA showed response or stabilization. The median time to disease progression after EGFR-TKIs treatment was 13.5 months in PIK3CA and not reached in T790M. Conclusions: The de novo T790M, KRAS and PIK3CA mutation was detected in 24%, 14.4% and 26.4% using ICP in cfDNA. In our study, the KRAS and EGFR mutation may not be mutually exclusive and PIK3CA mutations may be a factor associated with metastatic sites rather than predictive factor for EGFR-TKIs. In addition, we suggested that although the clinical presentation is more aggressive in patients with de novo T790M and PIK3CA mutation, the EGFR-TKIs could be used in patients who present with both activating EGFR mutations and those mutations.