Intratumor heterogeneity and tissue distribution of KRAS mutation in non-small cell lung cancer: implications for detection of mutated KRAS oncogene in exhaled breath condensate

Abstract

PurposeMutated KRAS oncogene in exhaled breath condensate (EBC) can be a genetic marker of non-small cell lung cancer (NSCLC). However, a possibility of inhomogeneous distribution in cancer tissue and intratumor heterogeneity of KRAS mutation may decrease its significance. We investigated a status of KRAS point mutation and its sequence at codon 12 in 51 NSCLC patients after tumor resection. The comparison of KRAS mutation status between EBC–DNA and cancer tissue was performed in 19 cases.MethodsFive cancer tissue samples from disparate tumor regions and one from normal lung were harvested at surgery. EBC was collected for DNA analysis the previous day. KRAS point mutations at codon 12 were detected using mutant-enriched PCR technique and pyrosequenced.ResultsForty-six cancers revealed concordance of KRAS mutation status: 27 contained mutated KRAS and 19 had only wild KRAS. Five NSCLCs revealed inhomogeneous distribution of KRAS mutation. Two different mutations were found in 14 NSCLCs and the most frequent one was G12D and G12V (n = 8). No mutated KRAS was found in normal lung. The concordance ratios of KRAS sequence in codon 12 between EBC–DNA and cancer were 18/19 for NSCLC patients and 11/12 for KRAS mutation positive NSCLC.ConclusionsIntratumor heterogeneity and inhomogeneous distribution of KRAS point mutation in codon 12 in cancer tissue can occur in NSCLCs. There was a high accordance between KRAS mutation status in EBC–DNA and cancer tissue in NSCLC patients what suggests usefulness of monitoring KRAS mutation in EBC–DNA as a biomarker of NSCLC.

Oncogenic driver mutations in non-small cell lung cancer: Past, present and future

“…As an example, RAS-independent activation of the PI3K/AKT/mTORC1 signaling pathway could be associated with resistance to KRAS inhibition[ 23 ]. Another mechanism of resistance could be the heterogeneous distribution of KRAS mutations in different tumor sites within the same patient[ 24 ]. Adaptive resistance also emerges under the selective pressure of KRAS TKIs.…”

Targeting KRAS: The Elephant in the Room of Epithelial Cancers

“…Another possible mechanism responsible for resistance to KRAS G12C inhibitors is represented by the presence of additional KRAS genetic alterations that can potentiate nucleotide exchange or impair inherent GTPase activity ( 94 ). Furthermore, the resistance to KRAS G12C inhibitors could be cause by the presence of a heterogeneous spectrum of KRAS mutations in the same patient ( 103 ).…”

Overcoming Resistance to Drugs Targeting KRAS Mutation

“… 49 Notably, the mutation status of KRAS gene could be heterogeneous in the same patient, which leads to the heterogeneous responses to K-Ras G12C inhibition across individuals, as well as in different tumors of the same patient ( Figure 3E ). 70 , 71 …”

“… 6 Aside from sustained primary KRAS G12C tumor regression, combination treatment provided significant protection against subsequent re-challenges with homogeneous KRAS G12D tumors, which implicated the establishment of antigen-specific memory responses. 6 Given that intratumoral KRAS mutation status could be heterogeneous between primary tumor and metastases in the same patient, 70 immunological memory induced by combinatory K-Ras G12C and checkpoint inhibition would be beneficial for patients across all stages of cancer ( Table 3 ).…”