Introduction

Lung cancer (LC) is the most common cause of global cancer-related mortality, with over a million deaths each year.¹ Non-small cell lung cancer (NSCLC) represents 85% of the cases, the most frequent histological subtypes are adenocarcinoma, squamous cell carcinoma, and large cell carcinoma.^2,3 NSCLCs are characterized by a unique pattern of genomic aberrations including mutations, amplifications, deletions, and rearrangements/fusions. Genetic profiling has identified driver mutations in over 80% of adenocarcinomas and approximately 47% of squamous cell carcinoma, many of which are relevant for clinical diagnosis and targeted therapy.^4,5

Currently, lung adenocarcinomas are treated on the basis of genomic aberrations to ensure better objective responses. Genomic testing of EGFR and ALK alterations is part of the standard diagnosis in NSCLC.⁶ Patients harboring EGFR mutations in advanced NSCLC benefit from receiving EGFR tyrosine kinase inhibitors (TKIs), like erlotinib, afatinib, gefitinib and osimertinib.⁷ Moreover, crizotinib has shown efficacy for patients with ALK-positive fusions. However, patients harboring sensitizing EGFR mutations develop TKIs resistance within one year.^8,9

Next-generation sequencing (NGS) has improved the diagnosis in NSCLC, and has increased the recognition of mutations like MET, BRAF and HER2 as novel targets for personalized therapies.¹⁰Furthermore, around 37% of the patients receive targeted therapy based in genomic profile.¹¹ Recently, the evaluation of tumor mutational burden by NGS has been a useful predictor of response to treatment.¹²

The mutation profile of many potentially actionable NSCLC genes in the Mexican population of patients remains largely unexplored. Previous studies by our group have described different NSCLC mutations and their relationship with clinical characteristics, such as never-smokers, female gender, wood smoke exposure and prognosis.^13,14EGFR mutations frequency vary among ethnic groups with 50-60% incidence in Asian patients, 10-15% in Caucasians, and 25-30% in Hispanics, in this population is particularly associated with female gender and never-smoker.^4,15This molecular heterogeneity of NSCLC is particularly high in Latin American countries, including Mexico as shown by the Latin-American Consortium for the Investigation of Lung Cancer (CLICaP, by its acronym in Spanish).^3,4The aim of this study was to characterize the presence of potentially actionable mutations in NSCLC in Mexican patients by targeted NGS, and compare the mutation frequencies among other populations.

Materials and methods

Results

Discussion

Lung cancer is the human neoplasm with the highest mutation rate after melanoma, with over 10 mutations/Mb for smokers.¹⁹ The presence of specific driver mutations has led to the development of targeted therapies for specific subsets of patients.^20,21In this study, we analyzed the mutation profile of NSCLC in the Mexican population, the association with clinical-pathological characteristics, therapeutic response and the contrast with other ethnic groups.

TP53 was the most frequently mutated gene in almost 50% of the patients and it was associated with former tobacco consumption. TP53 mutations had no prognostic value for OS of NSCLC patients. This tumor suppressor gene ranks first among the highly mutated genes in human cancers according to the lung cancer genome database.²² To date, TP53 is not a therapeutic target, nevertheless, it represents a prognostic factor of response. Recently, it has been shown that TP53 mutations correlate with resistance to chemotherapy, worse therapeutic responses and reduced OS of NSCLC patients depending on disease stage and sequencing platforms. Likewise, the biological role of TP53 mutations can be different according to tumor histology and smoking history.²³

TP53 mutations were concurrent with mutations in EGFR, MET, KRAS, and PDGFRA, while they were mutually exclusive with mutations in HNF1, APC and HER2. Concurrent mutations in TP53 and EGFR are frequent in NSCLC and may have impact on response rate, nonetheless, these results are diverse depending on the therapeutic approach. Recently, a comprehensive study by the lung cancer mutation consortium showed the adverse effect of concomitant mutations in TP53-mutated patients with targeted treatments for alterations in EGFR, ALK and ROS1, by developing resistance to chemotherapeutic agents. Moreover, the alterations imposed by TP53/KRAS co-mutations on cell-cycle regulation, control of DNA replication and repair result in higher neoantigen expression of neoantigens including PD-L1 upregulation, thereby increasing tumor immunogenicity.^24,25 Double-mutant tumors with TP53/KRAS co-mutations had significantly shorter OS and developed resistance to chemotherapy compared to wild type tumors. In contrast, TP53/KRAS co-mutation status was predictive of clinical benefit and better PFS in response to PD-1 immunotherapy.²⁶ The incidence of other TP53 co-mutations have been recently reported, nevertheless, their prognostic value remains unclear.²³

EGFR mutations are currently the main targetable oncogenic driver in the treatment of NSCLC patients, with improved response rates and less secondary effects than cytotoxic chemotherapy.²⁷ As previously reported, we found high prevalence of EGFR mutations, mainly exon 19 microdeletions and L858R point mutations in exon 21. In our study there was high concordance between results with qPCR based on Scorpions/ARMS technologies and the NGS platform in the detection of EGFR exon 19 deletions. EGFR mutations were associated with intermediate histological grade in advanced NSCLC. Consistently, a recent study indicated a correlation between moderately differentiated tumor grade and a higher frequency of EGFR mutations in metastatic lung adenocarcinomas. This modifies treatment selection, since patients with high grade or poorly differentiated tumors can be treated with chemotherapy or immunotherapy as first line treatment previous to obtaining the EGFR mutational status.²⁸

Other EGFR alterations found with low frequency were T790M mutation in exon 20 plus the A750P and G719A. Uncommon mutations are present in less than 10% of EGFR-mutant lung cancer and associated with high grade tumors, i.e. poorly differentiated, more aggressive phenotypes and could represent mechanisms of resistance to EGFR-TKI treatments.⁸ There are no targeted therapies for uncommon EGFR mutations, as their responses to TKIs are variable and the role in tumor biology is still unresolved.

In this study, MET exon 14 mutations were present in 20% of the patients, associated with female gender, pulmonary effusion and TP53 mutations. MET gene encodes a tyrosine kinase receptor that binds the hepatocyte growth factor. MET exon 14 codes for a portion of the juxtamembrane domain containing the binding site for ubiquitin ligases that participate in MET protein degradation. Mutations in MET exon 14 mutations cause exon 14 skipping, leading to constitutive signaling and oncogenicity.⁸ A recent study described a relationship between MET mutations, female gender and never smokers. Both MET mutations and amplifications show clinical benefit in NSCLC patients treated with TKIs not specifically designed for MET, having durable partial response with crizotinib and capmatinib and complete metabolic response with cabozantinib independently of histological subtype. Selective MET inhibitors have been developed such as tivantinib, onartuzumab and emibetuzumab with modest clinical benefits.^8,29

HER2 exon 20 mutations constitute 96% of the mutations in this gene and have been the most studied alterations in NSCLC. Conversely, other HER2 mutations have been described having prognostic value, including S310F/Y, D277G/H/V/Y and I655V.³⁰ Among the HER2 mutations in our study, I655V (exon 17) was detected with high frequency. This amino acid change in the transmembrane region increases tyrosine kinase activity leading to oncogenic signaling. I655V is present in different malignancies including breast, gastric and lung cancer. It correlates with aggressive tumor phenotype, poor prognosis and risk of cardiotoxicity during trastuzumab treatment of breast cancer.^8,31 However, there are few studies in lung cancer and without prognostic value.

In the present study, we found concurrence of HER2 mutations with intermediate histological grade and MET variants, but they were mutually exclusive with TP53 and EGFR mutations. There are no reports describing the association between HER2 mutations and tumor grade, although there is association with female gender, never smokers, adenocarcinomas, it has been reported that it confers a low sensitivity to traditional EGFR-TKIs.^8,30 HER2 mutations in NSCLC have a prevalence of 4% and may have higher clinical impact than gene amplification. Preliminary results from selective inhibitors for HER2 exon 20 mutations such as poziotinib had marked radiologic and clinical response. Additionally, several pan-EGFR irreversible inhibitors such as afatinib, neratinib, and dacomitinib have shown activity in NSCLC patients with HER2 mutations.^8,30,32

Adenomatous polyposis coli (APC) is a tumor suppressor gene mutated in 80% of colon carcinomas and less frequently in other malignancies including liver, breast and lung cancer.³² In our study, we found APC mutations in NSCLC that correlated with never smokers, were mutually exclusive with TP53 mutations and predicted poor prognosis. APC is part of the B-catenin degradation complex in the Wnt pathway. APC mutations induce nuclear B-catenin accumulation leading oncogene activation. APC mutations have been associated with nonsmokers in colorectal cancer.³³ These mutations are generally insertions/deletions that modify frameshifts, introduce premature stop codons and loss of function via truncation of APC protein. Current therapies for APC loss in cancer inhibit signaling through the canonical Wnt/B-catenin pathway downstream of APC or aim to restore normal APC expression. APC and TP53 mutations occur early in the initiation of carcinogenesis, but they are not documented as mutually exclusive alterations.³⁴ Although these alterations alone may not be sufficient to have a significant impacto on OS concomitant TP53 and APC mutations have been described as a more aggressive molecular phenotype with implications for worse prognosis in PFS/OS.⁴

There are differences in lung cancer incidence among different ethnic groups. While EGFR mutations appear in around 15% of North American and European patients, 40% of Asian patients, and between 2 to 14% of Afro-American patients, the frequency of EGFR mutations in Mexico is 27%.^4,35 In our study, the prevalence of EGFR mutations was 36.7% compared to 17% in Caucasians. Other important differences in mutation frequency between the two populations were present in known oncogenic drivers of NSCLC such as MET and HER2, while the frequency of KRAS mutation was higher in Caucasians as expected although not statistically significant. The incidence of KRAS mutations in NSCLC in Latin America is approximately 14-17% as reported by the CLICaP.⁴ MET mutation profile also differs in type and frequency according to ethnicity. In our study, HER2 mutations were present in 11.1% of the Mexican patients in contrast to 2.2% in Caucasians and 3.9% in Asians. Similarly to EGFR mutations, HER2 mutations are associated with adenocarcinoma histology, female gender and never smokers and have favorable response to TKI and antibody treatments.²³ A higher incidence of HER2 mutations in our population opens the opportunity to improve response rates and overall survival with novel targeted therapies.

Conclusions

This study provides a profile of somatic mutations for NSCLC in the Mexican population. The main genomic alterations were present in TP53, EGFR, KRAS, MET, PDGFRA, HNF1A, APC, HER2 and MSH6. This mutation profile shows differences with other ethnic groups. Further studies are warranted to evaluate the germline molecular features underlying the relationship between ethnicity, somatic mutation rates, clinical responses and survival of NSCLC patients.