Introduction

Non-small cell lung cancer (NSCLC) represents the predominant subtype of lung cancer, accounting for approximately 85% of all cases [1-2]. Despite significant advancements in diagnostic techniques and therapeutic interventions, NSCLC remains a principal cause of cancer-related mortality worldwide. The complexity of the molecular pathways involved in the pathogenesis of NSCLC necessitates a deep understanding of these mechanisms. Such knowledge is essential for the development and optimization of targeted therapies, which hold the potential to improve patient outcomes significantly [1, 3].

Mechanisms of Oncogenesis during abnormal genetic alterations (AGA)

There are many abnormal genetic aberrations already identified in NSCLC, at least for ten of them we have identified a targeted therapy while for the others research is ongoing. Epidermal growth factor receptor (EGFR) is a dimeric membrane protein and is expressed in more than 60% of NSCLCs. Binding to its ligand facilitates the formation of a dimer and phosphorylation of the tyrosine residues. The process activates the intracellular downstream signaling through MAPD and PI3K pathways, leading to cancer cell proliferation, differentiation, migration, and survival [1, 4]. Approximately 20% of NSCLC patients carry activating mutations in EGFR [4-6]. The most common mutations in non-small cell lung cancer (NSCLC) include deletions in exon 19 (Ex19del) and the L858R point mutation within exon 21. EGFR mutations are more prevalent among individuals of East Asian ethnicity, females, and never-smokers, and are more frequently identified in adenocarcinoma subtypes [1,3,7]. Interestingly, current research suggests that NSCLC patients with EGFR mutations exhibit a better overall survival (OS) outcome compared to those with wild-type EGFR, regardless of whether they receive targeted EGFR therapy. EGFR mutation appears to be an independent predictor of better outcomes. EGFR-mutated NSCLC cells are highly sensitive to EGFR Tyrosine Kinase inhibitors (TKI) [3]. There are additional EGFR mutations that are less common in exons 18 and 20 that respond to the TKI afatinib [4] or insertion in exon 20 that conferee a poor response to TKI and have now new therapies like chemothereapy and amivantamab a bispecific antibody [5]. 

Anaplastic lymphoma kinase (ALK) is a transmembrane receptor tyrosine kinase predominantly expressed in the central and peripheral nervous systems of developing embryos, with expression levels significantly decreasing after birth. ALK gene rearrangements occur in approximately 3-8% of non-small cell lung cancer (NSCLC) cases, particularly in adenocarcinomas, affecting predominantly younger patients, males, and never or light smokers. The EML4 and ALK genes are closely located on the short arm of chromosome 2. The intrachromosomal rearrangement resulting in the EML4-ALK translocation leads to the constitutive dimerization of the ALK kinase domain, which activates downstream cell signaling pathways responsible for inhibiting apoptosis and promoting cellular proliferation. Research has suggested that the ALK fusion gene tends to be mutually exclusive with EGFR and KRAS mutations. Consequently, targeting the EML4-ALK fusion gene has been a focus in the treatment of NSCLC [1, 6]. The proto-oncogene tyrosine-protein kinase (ROS) participates in embryonic development and acts as an initiator of signaling events for the differentiation of epithelial tissues. The incidence of ROS1 rearrangement is about 1-2% among NSCLC patients [6,7]. It is more reported in females, nonsmokers, and younger age. ROS rearrangement, by forming phosphotyrosinerecruitment sites in the terminal tail of ROS, leads to protein kinase-activity dysregulation and abnormal activation of signaling pathways involved in cell proliferation, growth, and survival [8]. However, ROS1 rearrangements are not associated with poor prognosis. It is reported to have a higher incidence of the development of thromboembolic events when compared to EGRF or KRAS mutation and the general NSCLC population despite no mortality differences being found [9,10]. 

Mesenchymal-Epithelial Transition (MET)

The Mesenchymal-Epithelial Transition (MET) protooncogene, which encodes a receptor tyrosine kinase, is a transmembrane receptor expressed in the epithelial cells of multiple organs, including the liver, pancreas, and bone marrow. MET recognizes hepatocyte growth factor (HGF) as a ligand and regulates essential cellular processes. Acting as both a pleiotropic factor and a cytokine, HGF promotes cell proliferation, survival, differentiation, and morphogenesis [11-13].

Current studies indicate that diverse oncogenic alterations of MET, including mutations, amplification, overexpression, chromosomal rearrangements, and fusions, contribute to the development of cancer. MET exon 14 skipping is the most prevalent point mutation identified in non-small cell lung cancer (NSCLC), and it is associated with a poor prognosis [11, 14]. 

The purpose of this paper is to review the most significant clinical data available for key genetic aberrations in lung cancer, examining the benefits of the latest therapies on clinical outcomes and the adverse effects that patients may experience during treatment.

EGFR

EGFR tyrosine kinase inhibitors (TKIs) are recommended as the first-line treatment for advanced non-small cell lung cancer (NSCLC) patients with EGFR-activating mutations. Additional EGFR mutations that lead to TKI resistance frequently contribute to disease progression. Although lung cancer remains challenging to treat and is usually incurable in its advanced stages, the discovery of EGFR-activating mutations has transformed the perception and management of this disease. The response to EGFR TKIs has fostered hope that lung cancer might become curable in the future.

In 2017, Soria et al. published the results of the FLAURA trial, which evaluated the efficacy of osimertinib compared to standard EGFR tyrosine kinase inhibitors (TKIs), gefitinib or erlotinib, in the treatment of patients with locally advanced or metastatic non-small cell lung cancer (NSCLC). The study included patients who had not received prior treatment and were confirmed to have EGFR exon 19 deletions or L858R mutations. Importantly, the inclusion criteria allowed for patients with central nervous system (CNS) metastases, provided they were in a stable neurological condition.

The trial demonstrated a significant improvement in median progression-free survival (PFS) with osimertinib, which was 18.9 months compared to 10.2 months for patients treated with standard EGFR-TKIs (hazard ratio for disease progression or death, 0.46; 95% confidence interval [CI], 0.37 to 0.57; P<0.001). Furthermore, the overall survival (OS) rate at 18 months was notably higher in the osimertinib group at 83% (95% CI, 78 to 87) versus 71% (95% CI, 65 to 76) in the standard EGFR-TKI group (hazard ratio for death, 0.63; 95% CI, 0.45 to 0.88; P = 0.007, although nonsignificant in the interim analysis). Adverse events of grade 3 or higher occurred less frequently with osimertinib than with standard EGFR-TKIs (34% vs. 45%). These results were pivotal in establishing osimertinib as a first-line treatment option for patients with EGFR-mutated advanced NSCLC.

Notably, resistance to first- and second-generation EGFR tyrosine kinase inhibitors (TKIs), primarily due to the T790M mutation, typically emerges within 8-14 months of treatment initiation. The third-generation TKI, osimertinib, was developed to address this issue. Fourth-generation drugs, which are still under development, are anticipated to overcome multiple resistance mechanisms, including those observed with third-generation TKIs. The ADAURA trial, led by Wu et al., evaluated the efficacy of osimertinib in patients with completely resected EGFR mutation– positive non-squamous NSCLC. The primary endpoint was disease-free survival (DFS) among patients with stage II to IIIA disease. A total of 682 patients were randomized in a 1:1 ratio to receive either osimertinib or placebo for three years. At 24 months, the DFS rate in the osimertinib group was 89% (95% CI, 85 to 92) compared to 52% in the placebo group (95% CI, 46 to 58), with an overall hazard ratio for disease recurrence or death of 0.20 (99.12% CI, 0.14 to 0.30; P<0.001). Additionally, at the same time point, 98% of patients in the osimertinib group (95% CI, 95 to 99) and 85% of those in the placebo group (95% CI, 80 to 89) were alive without central nervous system disease, with an overall hazard ratio for disease recurrence or death of 0.18 (95% CI, 0.10 to 0.33).

The authors concluded that in patients with stage IB to IIIA EGFR mutation–positive NSCLC, DFS was significantly longer for those receiving osimertinib compared to those who received placebo. The latest updates from this trial also suggest a minimal, yet statistically significant, improvement in overall survival (OS).

Trials are currently assessing the role of added chemotherapy for metastatic disease to improve outcomes, but the results have been mixed so far. Longer-term survival data are necessary before incorporating chemotherapy into the initial treatment strategy for EGFR-mutant NSCLC. In the FLAURA2 trial, an open-label study involving 557 patients with advanced EGFR-mutated NSCLC, the initial treatment combining osimertinib with platinum-pemetrexed chemotherapy showed an improvement in progression-free survival (PFS) compared to osimertinib alone (29.4 months versus 19.9 months). At 24 months, overall survival (OS) data were immature, but there was a nonsignificant trend favoring the osimertinib-chemotherapy combination (hazard ratio 0.9, 95% CI 0.65-1.24). However, grade =3 adverse events were more common in the osimertinib-chemotherapy group (64% versus 27%). These findings suggest a potential benefit in PFS with the addition of chemotherapy to osimertinib treatment, though the increase in severe adverse effects and the lack of significant improvement in OS at the interim analysis warrant cautious interpretation and further investigation.

An open-label, randomized phase 2 clinical trial evaluated the efficacy of osimertinib alone versus its combination with carboplatin-pemetrexed in patients with EGFR mutation-positive NSCLC who experienced disease progression associated with the T790M resistance mutation during first-line EGFR-TKI therapy. The study found that the median progression-free survival (PFS) was 15.8 months for the osimertinib monotherapy group compared to 14.6 months for the combination therapy group, with a hazard ratio of 1.09 (95% confidence interval: 0.51-2.32; P = .83). Median overall survival (OS) was not reached in either group. The overall response rate was 71.4% in the osimertinib monotherapy group and 53.6% in the combination group. The frequency and severity of known adverse events in the combination group were comparable to those previously reported for carboplatin and pemetrexed, and no novel adverse events were observed during the study. The addition of chemotherapy to osimertinib as a second-line treatment did not prolong survival but was found to be generally tolerable. This suggests that while the combination therapy does not offer a significant survival benefit over osimertinib monotherapy, it remains a viable treatment option for patients who can tolerate the regimen.

A phase II study done assessed the efficacy of osimertinib in patients with EGFR mutation-positive NSCLC in whom systemic disease (T790M-negative) progressed after treatment with first- or second-generation EGFR TKIs and platinum-based chemotherapy. The primary end point was overall response rate (ORR). From August 2020 to February 2021, 55 patients from 15 institutions were enrolled in the study. The ORR for primary analysis was achieved in 16 patients (29.1 %; 95 % CI, 17.6-42.9), which exceeded the threshold response rate necessary for analysis. Stable disease (SD) was found in 16 patients (29.1 %), and progressive disease, in 18 (32.7 %). The median length of PFS was 4.07 months (95 % CI 2.10-4.30), and the rate of 12-month PFS was 17.3 %. Osimertinib demonstrated modest antitumor activity against progressive EGFR T790M-negative disease [17].

The BOOSTER trial, an open-label randomized phase II study, investigated the efficacy and safety of combining osimertinib with antiangiogenic therapy using bevacizumab in patients with EGFR-mutant advanced NSCLC who acquired T790M mutations after failure on previous EGFR TKI therapy. The primary endpoint of the trial was investigator-assessed progression-free survival (PFS), while secondary endpoints included overall survival (OS), objective response rate (ORR), and adverse events (AEs). Between May 2017 and February 2019, 155 patients were randomized into two groups: 78 received the combination therapy of osimertinib 80 mg daily and bevacizumab 15 mg/kg every 3 weeks, and 77 received osimertinib alone. After a median follow-up of 33.8 months (interquartile range: 26.5-37.6 months), 129 (83.2%) PFS events were reported in the intention-to-treat population.

The results showed no significant difference in median PFS between the combination therapy group (15.4 months; 95% CI: 9.2-18.0 months) and the osimertinib alone group (12.3 months; 95% CI: 6.2-17.2 months; stratified log-rank P = 0.83), with a hazard ratio (HR) of 0.96 (95% CI: 0.68-1.37). Median OS was also similar between the groups, being 24.0 months (95% CI: 17.8-32.1 months) in the combination arm and 24.3 months (95% CI: 16.9-37.0 months) in the osimertinib arm (stratified log-rank P = 0.91), with an HR of 1.03 (95% CI: 0.67-1.56). The study shows no significant improvements in progression-free survival (PFS) or overall survival (OS) compared to osimertinib alone for the broader patient population. However, an exploratory analysis highlighted a notable interaction between smoking history and treatment efficacy for PFS. Specifically, smokers benefited more from the combination therapy, showing a hazard ratio (HR) of 0.52 (95% CI: 0.30-0.90), indicating a reduced risk of disease progression or death, whereas never smokers had an HR of 1.47 (95% CI: 0.92-2.33), suggesting a potential disadvantage.

The objective response rate (ORR) was consistent across both treatment arms at 55%, but the median time to treatment failure was significantly shorter in the combination group than in the osimertinib-alone group (8.2 months vs. 10.8 months, respectively; P = 0.0074). This finding suggests that while the combination therapy may initially inhibit tumor growth effectively, its benefits may diminish quicker than with osimertinib alone.

Regarding safety, the incidence of grade =3 treatmentrelated adverse events (TRAEs) was higher in the combination therapy group (47%) compared to the osimertinib-alone group (18%). This aligns with previous reports, underscoring that while the combination of osimertinib and bevacizumab is tolerable, it poses a higher risk of severe side effects.

The differential impact of the combination therapy based on smoking status underscores the complexity of lung cancer treatment and suggests that personalized approaches could be crucial in optimizing therapeutic strategies. Further research is necessary to understand the mechanisms behind these differences and to determine optimal dosing strategies or alternative combinations of targeted therapies, particularly for specific patient subgroups like smokers.

Resistance to EGFR tyrosine kinase inhibitors (TKIs) in the treatment of non-small cell lung cancer (NSCLC) can be classified into two main categories: intrinsic (or primary) resistance and extrinsic (or secondary) resistance. Intrinsic resistance refers to the initial ineffectiveness of EGFR-TKIs, even in the presence of EGFR mutations that typically predict a favorable response to these drugs. Although the exact mechanisms underlying intrinsic resistance are not fully understood, it has been associated with non-classical sensitizing EGFR mutations that do not respond to standard EGFR-TKIs as effectively as classical mutations like exon 19 deletions or the L858R mutation in exon 21.

Secondary or acquired resistance, on the other hand, typically develops after prolonged exposure to EGFR-TKIs. Several molecular mechanisms contribute to this type of resistance. Among these, mutations in exon 20 of the EGFR gene, particularly exon 20 insertions, are notable for their role in conferring resistance to first- and second-generation EGFR-TKIs. These exon 20 insertions occur in approximately 1-10% of cases and represent a significant challenge in the management of EGFRmutant NSCLC, necessitating alternative therapeutic strategies or the development of next-generation inhibitors that can effectively target these resistant mutations.

Ongoing research is exploring novel combination therapies that can circumvent medication resistance due to EGFR mutations, a prevalent issue in the treatment of non-small cell lung cancer (NSCLC). Among these studies, the MARIPOSA trial (NCT04487080) is a phase 3, multicenter, randomized study that compares the efficacy and safety of the combination therapy of amivantamab and lazertinib versus single-agent osimertinib as first-line treatment for patients with EGFR-mutant NSCLC. Amivantamab is an EGFR-MET bispecific antibody with immune cell-directing activity, which targets both activating and resistance EGFR mutations as well as MET mutations and amplifications.

In another study, the ongoing CHRYSALIS trial (NCT02609776), amivantamab in combination with lazertinib, a potent, brain-penetrant third-generation EGFR TKI, has shown antitumor activity in both treatment-naive patients and those who have relapsed on osimertinib. Further demonstrating the potential of these innovative approaches, a phase I study conducted in October 2023 examined the use of amivantamab plus chemotherapy for advanced NSCLC with EGFR exon 20 insertions. In a randomized trial involving 308 patients with advanced NSCLC harboring EGFR exon 20 insertions and who had not received previous systemic therapy, those assigned to the targeted combination of amivantamab and chemotherapy experienced a significantly longer progression-free survival compared to those receiving chemotherapy alone (11.4 versus 6.7 months).

These findings suggest that integrating targeted agents like amivantamab with either novel TKIs like lazertinib or with chemotherapy could represent a promising strategy to overcome resistance mechanisms in EGFR-mutant NSCLC, potentially leading to improved clinical outcomes for this challenging patient population [19].

In summary, there are exciting developments ongoing for patients with EGFR-mutated non-small cell lung cancer (NSCLC). The treatment landscape is evolving from the use of osimertinib as monotherapy to exploring its use in combination with chemotherapy. Furthermore, the potential introduction of new therapeutic agents like amivantamab and lazertinib as frontline treatments represents a significant advancement. These innovative approaches aim to enhance treatment efficacy, manage resistance mechanisms, and improve clinical outcomes.

Table 1: Landmark trial of EGFR targeted therapy.

ALK

The therapeutic landscape has been significantly changed with the introduction of ALK inhibitors to clinical trials and encouraging improvements in patient prognoses since the identification of EML4-ALK fusion in non-small cell lung cancer (NSCLC). Cryzotinib was initially recognized as the chosen therapeutic intervention for ALK fusions, which in turn other medications to participate in clinical trials with the objective of acquiring improved disease management and results.

The 2017 J-ALEX study, led by Hida et al., was an important phase 3 trial that played a significant role in the approval of ALK-targeted therapy. Patients from Japan who had one prior chemotherapy regimen or were chemotherapy-naive but had ALKpositive NSCLC were the primary participants in this study. Until disease progression, intolerable toxicity, death, or withdrawal, 207 patients were randomly assigned to receive oral alectinib or crizotinib.

PFS was the principal outcome measure utilized in this research. Patients who were administered alectinib had a significantly longer PFS than those who were administered crizotinib (hazard ratio [HR] 0.37, 95% confidence interval [CI] 0.26-0.52; median PFS 34.1 months versus 10.2 months with crizotinib), according to a subsequent analysis of the data. With the exception of the median OS, neither treatment arm achieved a superior overall survival (OS) rate than the other at the time of the final OS analysis in late 2020 (HR 1.03, 95% CI 0.67-1.58, P = 0.9105; median OS did not reach 0.67). A possible limitation of this study went beyond this demographic cohort, as the study’s representation was almost exclusively of the Asian population.

Overall, additional research is required to determine the long-term efficacy and generalizability of alectinib beyond the J-ALEX trial, where it demonstrated a superior PFS in comparison to crizotinib. 

Table 2. ALK targeted therapy.

In the ongoing development of treatments for ALK-positive non-small cell lung cancer (NSCLC), another ALK inhibitor, brigatinib, has shown promise when compared to crizotinib. The ALTA-1L trial, led by Camidge et al., involved randomly assigning patients with advanced ALK-positive NSCLC who had not previously received any ALK inhibitors. The patients were given either brigatinib or crizotinib with the primary endpoint being progression-free survival (PFS).

The results demonstrated a higher rate of PFS with brigatinib compared to crizotinib. The estimated 12-month PFS for patients receiving brigatinib was 67% (95% confidence interval [CI], 56 to 75) versus 43% (95% CI, 32 to 53) for those receiving crizotinib, with a hazard ratio for disease progression or death of 0.49 (95% CI, 0.33 to 0.74; P<0.001). These findings led the authors to conclude that brigatinib significantly prolongs PFS compared to crizotinib among patients with ALK-positive NSCLC who have not previously received an ALK inhibitor. This study underscores the effectiveness of brigatinib as a valuable therapeutic option for patients with this specific genetic profile, potentially offering improved outcomes over the previously preferred crizotinib.

In a large multicenter, open-label, randomized phase 3 trial conducted across 120 centers in 21 countries, 290 patients with advanced, recurrent, or metastatic ALK-positive NSCLC were enrolled between July 25, 2016, and November 12, 2018. This study, led by Leora Horn et al., investigated the efficacy of ensartinib compared to crizotinib. Patients, aged 18 years or older (median age, 54 years; range, 25-90 years), were randomized in a 1:1 ratio. In the ITT (intention-to-treat) population, the median PFS was significantly longer with ensartinib than with crizotinib

(25.8 [range, 0.03-44.0 months] vs 12.7 months [range, 0.0338.6 months]; hazard ratio, 0.51 [95% CI, 0.35-0.72]; log-rank P < .001), with a median follow-up of 23.8 months (range, 0-44 months) for the ensartinib group and 20.2 months (range, 0-38 months) for the crizotinib group. In the mITT population, the median PFS in the ensartinib group was not reached, and the median PFS in the crizotinib group was 12.7 months (95% CI, 8.9-16.6 months; hazard ratio, 0.45; 95% CI, 0.30-0.66; log-rank P < .001). The intracranial response rate was 63.6% (7 of 11) with ensartinib vs 21.1% (4 of 19) with crizotinib for patients with target brain metastases at baseline. PFSl for patients without brain metastases was not reached with ensartinib vs 16.6 months with crizotinib as a result of a lower central nervous system progression rate (at 12 months: 4.2% with ensartinib vs 23.9% with crizotinib; cause-specific hazard ratio, 0.32; 95% CI, 0.16-0.63; P = .001). Frequencies of treatment-related serious adverse effectsvents

(ensartinib: 11 [7.7%] vs crizotinib: 9 [6.1%]), dose reductions (ensartinib: 34 of 143 [23.8%] vs crizotinib: 29 of 146 [19.9%]), or drug discontinuations (ensartinib: 13 of 143 [9.1%] vs crizotinib: 10 of 146 [6.8%]) were similar, without any new safety signals. (254)

For patients with newly diagnosed, ALK-positive non-small cell lung cancer (NSCLC), the recommendation has shifted towards using a next-generation ALK inhibitor as the first-line treatment over crizotinib, due to the superior efficacy and safety profiles of these newer agents. Among the second-generation ALK inhibitors, alectinib is often suggested due to the availability of longer-term follow-up data from clinical trials, which has demonstrated its effectiveness and tolerability. However, it is important to note that direct comparisons between second-generation ALK inhibitors have not been extensively performed, making it challenging to definitively rank one over the others based solely on direct headto-head data. As such, other second-generation inhibitors such as brigatinib and lorlatinib are also recognized as viable first-line options. Each of these medications has shown significant efficacy in clinical settings and can be considered depending on individual patient profiles, such as the presence of brain metastases, specific mutation patterns, and potential side effects. This approach allows for personalized treatment planning to optimize outcomes for patients with ALK-positive NSCLC.

The CROWN trial, a phase 3 study led by Shaw et al., evaluated lorlatinib against crizotinib in patients with previously untreated advanced ALK-positive NSCLC. Lorlatinib demonstrated a significantly higher overall response rate (ORR) of 76% (95% CI, 68 to 83) compared to 58% (95% CI, 49 to 66) in the crizotinib group. Notably, lorlatinib achieved 71% rate of intracranial complete response, highlighting its effectiveness in treating patients with CNS involvement-a common complication in NSCLC. The most frequent adverse events associated with lorlatinib were hyperlipidemia, edema, peripheral neuropathy, and cognitive effects. These findings underscore lorlatinib’s potential as a superior first-line option for this patient population, particularly for those with a significant risk of or existing brain metastases.

Ceritinib was the first second-generation ALK inhibitor approved specifically for the treatment of NSCLC patients resistant to crizotinib. It effectively inhibits the L1196M and G1269A ALK mutations, which are among the most common mechanisms of resistance to crizotinib. This makes cells expressing ALK significantly more sensitive to ceritinib compared to crizotinib, providing a robust treatment option for patients who develop resistance. In current clinical studies, ALK-positive NSCLC, other second-generation ALK inhibitors such as alectinib, brigatinib, and PF-06463922 (lorlatinib) are currently under development. Each of these agents targets different crizotinib-resistant ALK mutations, enhancing the potential for tailored treatment strategies based on the genetic profile of the tumor. The genetic identification of crizotinib-resistant mutations is key for selecting the most effective treatment strategy to overcome resistance and improve progression-free survival in NSCLC patients. This guidance emphasizes the importance of personalized medicine in the management of cancer, allowing for more targeted and effective interventions based on individual tumor genetics.

ROS 1  

ROS1 gene fusions account for approximately 1-2% of all cases of non-small cell lung cancer (NSCLC). Similarly to ALK NSCLC, patients with ROS1+ NSCLC tend to have minimal smoking history and be of the female sex. In most cases, adenocarcinoma is the dominant histology [28]. There are currently fourthree target therapies for NSCLC with ROS-1 mutation. However, the resistance to current ROS1 inhibitors remains a significant clinical challenge. Focusing on the development of ROS-1 target therapy will serve a critical role in treating NSCLS with activating ROS1 gene mutations and improve the mortality.