In this study, MET exon 14 testing was analyzed in routine care settings. We showed that MET exon 14 mutations were a common event in the EGFR, KRAS, BRAF, ALK WT population justifying its systematic testing. Our routine pipeline uses ampliseq technology. When MET exon 14 testing became part of the molecular gene-set for lung cancer, we felt concerned by the issue of large deletion detection. The ampliseq technology uses primers designed to amplify small DNA fragments. This leads to intrinsic difficulties in calling large deletions either because amplicons are too small to be aligned or because primers match the deleted sequence. Therefore, we implemented a DNA-based algorithm to rescue the detection of large deletions using fragment analysis when NGS was negative. Two large deletions were identified (41bp and 65bp) by fragment analysis [16]. Fragment analysis is a fast, simple, and cost-efficient way to identify deletions. Although the sensitivity of this method was lower than that of NGS, the combination with amplicon-based NGS improved the detection of MET exon 14 alterations as previously described [19]. Other approaches exist to screen MET exon 14. One of the most powerful is to combine DNA and RNA-based detection as RNA sequencing is an efficient technic to detect splice-variant at transcript level. Moreover, as oncogenic transcripts are often highly expressed, it may more sensitive than DNA-based method [20]. Gene fusions represent promising targets in lung cancer and reliable detection of multiple gene fusions has become part of the routine screening [9]. This has impacted testing strategies. Indeed, as RNAseq becomes mandatory, MET exon14 skipping mutations that were missed by DNA sequencing would be rescued by RNA analysis. Moreover, RNAseq may also help classification of ambiguous splice mutations for which the functional impact on splicing is not clear. All together DNA/RNA based testing, seems to be the most accurate strategy to detect MET exon 14 mutation along with other targetable drivers. Here, 46 patients with MET exon 14 mutated tumors were identified. Most patients with MET exon 14 tumors are elderly patients with median age of 79 years [19]. This specificity underlines the importance of screening for MET exon 14 alterations in this population that is not always fit enough to receive chemotherapy. Half of the patients were smokers with a smoking history of 20 packs per years or more [21–23]. These clinical associations match to the current literature [24–25]. However, in a recent meta-analysis, based on 2661 NSCLC, patients with MET exon 14 mutations were less likely to associate with smoking history as compared to wild type patients (OR = 0.48, p = 0.008) [19]. These data highlight that MET exon 14 mutations affect both smokers and non-smokers, unlike most common oncogenic driver outside of KRAS. We collected real life data concerning patients’ treatments and response to MET inhibitors. In our cohort 11 patients received Crizotinib at different lines of treatment with a median PFS of 7.6 months. This was comparable to previous results. In PROFILE 1001 [26] ORR of 39% and median PFS of 7,3 months under Crizotinib with was the first MET TKI to receive FDA approval for MET exon14 NSCLC. More recently Capmatinib and Tepotinib have demonstrated ORR of 41% and 48% respectively. The median PFS was 9.7 months for capmatinib naif MET exon 14 patients and 8,5 months for Tepotinib [11, 12]. We noted a lower Capmatinib response than reported in GEOMETRY study (median PFS 3.0 versus 9.7 months respectively). However, in our study, 3/7 patients were previously treated with Crizotinib. Indeed, we cannot draw comparison because MET inhibitors pretreated patients were excluded from GEOMETRY. One patient had both MET amplification and MET exon 14 mutation. He almost achieved a complete response after 3 months of Crizotinib treatment. In the VISION trial, a better response of Tepotinib was reported in the 5 patients with concurrent MET exon 14 and MET amplification compared to MET exon 14 only (80% vs. 46% respectively). This finding suggests that this co-alteration may potentiate the activity of MET inhibitors. Regarding the response to ICIs in our patients, a median PFS of 4 months was noted. These results were comparable to those of the multicenter IMMUNOTARGET MET exon 14 cohort conducted by Mazières et al, [21]. We found a higher proportion of PD-L1 ≥ 50% compared to non-MET samples (p = 0.0012) consistent with previous reports [10]. However, we found no correlation between response and PD-L1 expression in the 13 patients treated with immunotherapy, which was consistent with the findings of Sabari et al, suggesting that PD-L1 has no predictive value in MET exon 14 patients [13]. On the other hand, almost all of them have PD-L1 (TPS) > 50%. We also noted a longer response to ICIs in heavy smokers. A PFS greater than 20 months was observed in 2 patients having smoked more than 30 pack-year smokers. High levels of tobacco intoxication may be associated with high mutational burden and an immunogenic microenvironment potentiating immunotherapy [27–29]. Additionally, we reported one case of severe hepatic toxicity in a patient treated with immunotherapy followed by Crizotinib. Other study reported similarly an increase in Grade 3 and 4 hepatitis with Crizotinib in immunotherapy-experienced subjects [11] and there is growing concern that immunotherapy followed by targeted therapies induces potentially severe immune-mediated adverse effects [30–31]. This data highlighted the importance of an early MET screening in order to choose the appropriate therapeutic sequence. Not detecting MET mutations is deleterious because patients with MET mutated tumors may have access to MET-targeted therapies and because patients could receive sub-optimal first line treatment such as ICIs monotherapy based on PD-L1 expression. Our testing and clinical experience led to the validation of a new workflow, first step includes the use of taqman probes for EGFR and KRAS frequent mutations and subsequent DNA and RNA sequencing panels in parallel. Altogether, the use of taqman probes and hotspots DNA and RNA panels covers all drivers in lung cancer at reasonable costs in a turnaround time of 10 days for a complete characterization.
Our study shows that the detection of MET mutations along with other potential drivers is feasible for all patients with advanced and metastatic NSCLC using optimized strategies at reasonable costs and rapid turnaround time. MET characterization is of major importance at diagnostic to optimize first line treatments as patients with MET mutations may be older, not fit for chemotherapy and low responders to immunotherapy despite high PDL-1. It has some limitations. First, the series is a real-life retrospective cohort with missing data for some patients and the number of patients with MET exon 14 tumors reflects reality. Patients were managed in different hospitals following recommended guidelines, but their treatments were different and MET inhibitors were not easily available in routine care at that time.