KRAS G12C Testing in Non-small Cell Lung Cancer (NSCLC)

KRAS mutations are molecularly diverse and heterogeneous, with various nucleotide changes occurring at different codons, and some being more prevalent than others in different types of cancer (Figure 1). KRAS mutations are generally mutually exclusive with other driver mutations such as EGFR and ALK, although co-mutations in other pathways have been observed [2].

In nonsquamous non-small cell lung cancer (NSCLC), activating mutations in KRAS are found in 25 to 30% of cases, representing the most prevalent oncogenic driver in NSCLC [3]. Among KRAS mutations, KRAS p.G12C (G12C), a single-nucleotide variant with glycine substituted by cysteine at codon 12, is the most frequent, with a prevalence of approximately 13% in lung adenocarcinoma [4].

However, geographic variation in prevalence has been reported, and specific mutations may be associated with smoking [4-6]. Though less common, additional KRAS mutations outside of codon 12, including codons 13 and 61, have been identified.

Mutations in codon 12 interfere with GTP hydrolysis, favoring the GTP-bound activated state and uncontrolled cell growth independent of extracellular stimulation (Figure 2). KRAS p.G12C mutations are generally considered driver events, which arise early in disease pathogenesis and stay throughout disease progression [8].

Because of the high frequency of its variants in cancers, KRAS has been an active area of research for therapeutic development. However, the high affinity of KRAS for GTP and the high intracellular concentration of GTP, along with the lack of binding pockets on GTP-bound KRAS, has led to the long-standing notion that mutant KRAS is challenging to target [1].

This challenge in developing effective approaches for targeting KRAS-mutant lung adenocarcinomas lies in the diversity of KRAS mutations. The heterogeneity in their biology and the mechanisms underlying this diverse biological behavior are not well understood [9].

Furthermore, co-alterations in KRAS may have significant implications for disease progression, and research on mechanisms of resistance, such as secondary mutations or alternate activation pathways, is a complex and evolving area. Thus, research focusing on co-alterations and mechanisms of resistance may elucidate complex interactions and provide insight into the development and progression of cancer.

Various testing methodologies are available for detecting KRAS mutations in NSCLC. These include polymerase chain reaction (PCR), Sanger sequencing, and next-generation sequencing (NGS), and formalin-fixed, paraffin-embedded (FFPE) specimens from tissue biopsies or cytology samples are often used in research. More recently, liquid biopsy has emerged as a viable option for molecular testing in the absence of tissue specimens.

NGS is becoming an invaluable method in clinical research, particularly with NSCLC, for its ability to simultaneously analyze multiple genes from limited tumor material. In order to systematically address the heterogeneity and study co-occurring genomic events, the use of NGS is essential. Additionally, related to the increasing number of genes of interest, broad molecular profiling with NGS has been shown to be more cost-effective than single-gene tests [11].

While multiple NGS platforms are available, each differing in panel size, tissue input requirements, and turnaround time, the success of the test is more likely when a technology is appropriately selected taking into consideration the tumor quality and quantity of the sample.