There was a time when patients with advanced non-small cell lung cancer (NSCLC) could only receive chemotherapy. However, its efficacy has reached a bottleneck and cannot be furthered. Happily, with the increasing understanding of molecular genetics, NSCLC has been subdivided into various molecular subtypes, and this has led to the birth of various molecularly targeted therapeutic agents. The application of targeted drugs has significantly improved the prognosis of NSCLC patients.
Chemotherapy has no place in the first-line treatment of patients with epidermal growth factor receptor (EGFR) mutations and mesenchymal lymphoma kinase (ALK) rearrangements unless the patient has a deletion of the druggable driver oncogene. 17 February 2015 Kumarakulasinghe et al. published a review in respirology that provides a comprehensive discussion of clinically relevant driver mutations, the latest molecular typing of lung adenocarcinoma and squamous carcinoma, the place of molecularly targeted drugs in therapy, and their resistance mechanisms.
Lung cancer is the number one killer in the oncology world. In 2014, 224,210 new lung cancer patients are expected to be diagnosed, most of them with advanced NSCLC, and for a long time, the only treatment for advanced NSCLC has been “platinum-based chemotherapy”. While this approach increased overall survival (OS) to some extent compared to best supportive care, it was limited to a 20% response rate and a median survival of 8-10 months.
As molecular genetics research continues to progress, attempts are slowly being made to identify the key genetic mutations that cause NSCLC. These genetic variants present on oncogenes encode signaling proteins that regulate cell proliferation and survival. The concept of oncogene dependence was born based on the idea that tumor survival is highly dependent on the expression of a single oncogene. The oncogene-dependent nature of NSCLC specifically has been demonstrated and has led to the creation of various specific molecularly targeted drugs.
Lung adenocarcinoma, which accounts for more than 50% of all NSCLC, is the most common tissue subtype. The significance of such staging is that the results of randomized trials have shown that the use of platinum-pemetrexed is more effective than platinum-gicitabine in non-squamous NSCLC. Lung adenocarcinoma can be further subdivided into additional subgroups based on relevant driver gene mutations (Figure 1). As of today, these driver genes include EGFR, KRAS, HER2, PIK3CA, BRAF, MET gene mutations and ALK, ROS1 and RET gene rearrangements.
Squamous cell carcinoma ranks second in NSCLC, accounting for approximately 20-30% of cases. In squamous cell carcinoma, EGFR gene mutations are very rare, and only gene amplification of fibroblast growth factor receptor-1 (FGFR1), mutation of discoid structural domain receptor 2 (DDR2) gene and amplification and mutation of PI3KCA gene are more common (Figure 1). Targeted therapeutic agents against the above mentioned variants are also really very effective in clinical practice.
Figure 1. Brief overview of genetic variants in non-small cell lung cancer
EGFR mutations
EGFR, also known as HER1 or ErbB1, is one of the four major members of the ErbB receptor family. over-expression of EGFR activates important downstream signaling pathways (e.g., ALK), leading to cell proliferation, survival, metastasis, and angiogenesis. Therefore, EGFR has been a hot topic in the research of NSCLC. The early small molecule EGFR tyrosine kinase inhibitors (TKI) like gefitinib and erlotinib were targeted at all NSCLC patients who had received prior chemotherapy when they were first introduced. And newly introduced EGFR TKI’s like afatinib and dacomitinib have built on this foundation.
Retrospective studies have shown that clinical characteristics such as Asian origin, female, adenocarcinoma, and little/no previous history of smoking can increase the sensitivity rate of EGFR TKI therapy. The molecular basis for this conclusion is that mutations in exons 18-21 (most commonly deletions in exon 19 and mutations in the L858R locus on exon 21) encode a large number of EGFR tyrosine kinases, with the above mutations accounting for 45% and 40% of the total mutation cases, respectively.
EGFR mutations are more common in patients with the aforementioned clinical features. Approximately 15% of Caucasians and 30-50% of East Asians with lung adenocarcinoma have EGFR mutations. For those East Asians without a smoking history, this percentage is as high as 50-60%.
Several studies have shown that treatment with TKI is superior to chemotherapy in terms of response rate (ORR), progression-free survival (PFS) and quality of life in patients with NSCLC with a primary sensitive EGFR mutation. The results of the Pan-Asian Study of ERSA (IPASS) showed that gefitinib was more effective than paclitaxel + carboplatin chemotherapy in selected NSCLC patients.
However, in EGFR wild-type patients, TKI treatment was not as effective, with a 1.5-month PFS losing out to 6.5 months in the chemotherapy arm. In other randomized studies, gefitinib, erlotinib, and afatinib improved ORR and PFS in patients with EGFR mutations, and these studies provide a basis for rational treatment of advanced NSCLC. Therefore, patients with advanced NSCLC should routinely undergo EGFR gene testing and choose whether to pursue first-line EGFR TKI therapy based on the mutation status.
EGFR TKI is generally well tolerated by patients. common side effects of EGFR TKI include acne in the form of rash, itchy skin and diarrhea. Compared to chemotherapy, grade 3-4 adverse reactions are rare, so dose adjustments and discontinuations are less common. The bad news is that all patients treated with TKI will eventually develop drug resistance and eventually lead to tumor progression and death. The good news is that some of the molecular mechanisms underlying resistance to TKI therapy have been identified through repeated biopsies. For example, the previously mentioned exon 20 (T790M) variant is present in approximately 50% of patients with acquired resistance.
In addition, MET amplification (5%), HER-2 amplification (8%), PI3K mutation (5%) and transformation of NSCLC to small cell lung cancer (18%) are also common mechanisms of drug resistance. Based on this, a new generation of molecularly targeted therapeutics began to target the above-mentioned acquired resistance pathways, such as T790M, HER2, MET and PI3KCA.
For example, the second-generation irreversible EGFR TKI afatinib and daclatinib are pan-ErbB inhibitors. This means they can inhibit EGFR mutation expression while also inhibiting T790M resistance variants. While preclinical studies have shown promising results, clinical studies of afatinib and daclatinib for the treatment of a generation of EGFR TKI resistance have not been as promising. One randomized study demonstrated that afatinib had comparable OS to placebo in patients with advanced non-small cell lung cancer treated with a first-generation EGFR TKI.
Another study demonstrated the same for daclatinib. However, in the latest guidelines, afatinib has been recommended as a first-line treatment option for non-small cell lung cancer with EGFR mutations.
The third generation EGFR TKI (CO-1686 and AZD9291) are more selective for T790M, with better clinical outcomes and less toxicity. Early studies have shown that CO-1686 and AZD9291 have achieved ORRs of 58% and 64%, respectively, in patients with advanced non-small cell lung cancer treated with a generation of EGFR TKI with T790M variants. These results further demonstrate the importance of timely molecular analysis to select the best treatment option at the stage of disease progression.
Echinoderm microtubule-associated protein-like 4 and mesenchymal lymphoma kinase fusion gene (EML4-ALK) gene recombination
The two genes EML4 and ALK are located on p21 and p23 of human chromosome 2, respectively. The inversion fusion of these two gene fragments enables tissues to express the novel fusion protein EML4-ALK, which can lead to tumorigenesis via the PI3K-AKT, MAPK and JAKSTAT pathways.
Thus, EML4-ALK is a newly identified driver gene for lung adenocarcinoma. ALK gene recombination is uncommon, accounting for only 4-7% of non-small cell lung cancers. It is more likely to be seen in patients with little/no previous smoking history and in younger patients. Its pathological type is often adenocarcinoma, more specifically alveolar and indolent cell carcinoma. Approximately 33% of NSCLC patients with non-EGFR and KRAS mutations will have EML4-ALK mutations. Moreover, the EML4-ALK mutation is strongly exclusive, meaning that when it is mutated, other driver genes tend not to mutate.
ALK inhibitors include crizotinib (crizotinib), ceritinib (ceritinib) and alectinib. in a phase III study, crizotinib was used in patients with advanced NSCLC with ALK mutations in primary therapy and showed a significant improvement in ORR (45%: 74%) and PFS (7 months: 10.9 months) compared with chemotherapy . In another phase III study, the clinical efficacy of crizotinib in patients with treated advanced NSCLC with ALK mutations was also significantly better than that of single-agent chemotherapy (ORR 65%:20%; PFS 7.7 months:3 months).
Multiple mechanisms of resistance to crizotinib are also slowly being reported. For example, secondary mutations in the ALK tyrosine kinase structural domain (most commonly the L1196M mutation), increased ALK copy number, and the emergence of new driver genes (e.g., EGFR and KRAS mutations). The understanding of drug resistance mechanisms determines the future direction of targeted drug development.
Ceritinib is a second-generation ALK inhibitor that can be used in ALK-positive tumors that have failed primary therapy or crizotinib treatment. Its ORR is 66% and 55% for primary and crizotinib-naïve patients, respectively. Recently, the U.S. Drug and Food Administration (FDA) approved ceritinib for patients with ALK-positive metastatic non-small cell lung cancer and crizotinib-treated non-small cell lung cancer failure. In another clinical trial, alectinib treated ALK-positive primary patients with an impressive ORR of 93.5%.
ROS1 chromosomal translocation
ROS1, known as c-ros proto-oncogene, is a transmembrane receptor tyrosine kinase gene. translocation of the ROS1 chromosome activates ROS1 kinase activity. rOS1 is often seen in young people who have never smoked. The usual pathological type is adenocarcinoma. Mutations account for about 3% of all NSCLC. Clinical studies have shown that crizotinib is effective in ROS1-positive NSCLC with an ORR of 56%.
BEAF gene mutation
The BRAF gene encodes a serine/threonine protein kinase and is a member of the RAF family. BRAF mediates tumorigenesis by phosphorylating MEK and activating the downstream ERK signaling pathway. Mutations in the BRAF gene occur in only 1 to 3% of non-small cell lung cancers, and 50% of these are BRAF V600E locus mutations.
BRAF mutations are more likely to occur in adenocarcinoma, and BRAF V600E is more common in women and non-smoking patients. BRAF inhibitors are dabrafenib and vemurafenib, and they are effective in patients with NSCLC with BRAF V600E mutations.
In phase I/II studies, dabrafenib in patients with treated NSCLC with BRAF V600E mutation could have a 40% response rate and 60% disease control rate. Based on these impressive results, the FDA granted breakthrough therapy designation to darafenib for patients with advanced NSCLC with BRAF V600E mutation-positive disease who have received at least one prior platinum-containing chemotherapy regimen.
MET overexpression
MET is a complex kinase receptor whose over-activation is closely related to tumorigenesis, progression, prognosis and regression. Over-activation of tyrosine kinase leads to activation of its downstream signaling pathways, ultimately leading to cell transformation, proliferation and resistance to apoptosis, promoting cell survival, causing tumor metastasis, angiogenesis and epithelial-mesenchymal transition (EMT). Overexpression of MET can occur in approximately 7% of NSCLC patients.
Preliminary data suggest that crizotinib may have a 33% response rate for treatment of MET overexpressed NSCLC. For those patients with high MET overexpression, the response rate was 67%.
KRAS gene mutations
KRAS is a member of the RAS family, and mutations in KRAS continue to stimulate cell growth and prevent cell death, leading to tumorigenesis. Patients with NSCLC with KRAS mutations have a higher chance of recurrence and metastasis. Adenocarcinoma, history of smoking and white race are risk factors for KRAS mutations. There are no drugs for advanced NSCLC with KRAS mutations, and research by major companies has focused on downstream pathways of KRAS, such as MEK.
In a randomized study, the oral MEK inhibitor selumetinib was used in combination with chemotherapy in patients with treated KRAS-mutated non-small cell lung cancer. The ORR (37%: 0%), PFS (5.3 months: 2.1 months), and OS (9.4 months: 5.2 months) were significantly improved compared with chemotherapy alone.
HER-2 gene mutation
HER-2 (also known as ErbB2), like EGFR, is one of the four major members of the ErbB receptor family. HER-2 is a proliferation driver that is abnormally expressed in NSCLC as amplification, overexpression and mutation. In NSCLC, HER-2 amplification and HER-2 overexpression account for approximately 20% and 6%-35%, and HER-2 mutations account for 1%-2%. The majority of NSCLC patients presenting with HER-2 mutations are women, nonsmokers, and adenocarcinoma patients.
Although HER-2 inhibitors (such as trastuzumab, patolizumab and lapatinib) are effective in breast cancer for HER-2-positive patients, this does not apply to lung cancer. A study comparing chemotherapy alone with chemotherapy combined with trastuzumab for HER-2-positive non-small cell lung cancer did not show a statistically significant difference.
There are still ongoing studies of trastuzumab and afatinib in patients with HER-2-positive non-small cell lung cancer, so we’ll just have to wait and see.
RET translocation
The RET gene can be fused to translocations such as CCDC6, KIF5B, NCOA4 and TRIM33. This phenomenon can occur in 1% of patients with adenocarcinoma. However, in younger, non-smoking patients, the probability can be elevated to 7-17%. Tyrosine kinase inhibitors such as cabozantinib (cabozantinib), vandetanib (vandetanib), sunitinib (sunitinib), and ponatinib (ponatinib) have long been approved for other RET-positive tumors. Clinical trials for non-small cell lung cancer are also in full swing.
In addition, regorafenib and lenvatinib are also RET inhibitors.
NTRK1 (neurotrophic tyrosine kinase type 1 receptor) gene fusion
The NTRK1 gene encodes a high-affinity nerve growth factor receptor (TRKA) that promotes cell differentiation. both MRRIP-NTRK1 and CD74-NTRK1 fusions can lead to structural alterations in TRKA kinase activity, which can exert oncogenic effects. NTRK1 fusions have been reported to be found in approximately 3% of NSCLC patient tumors without other known oncogene mutations. nTRK1 inhibitors are in clinical trials, such as crizotinib, ARRY-470, and letatinib (lestaurtinib).
FGFR1 (fibroblast growth factor receptor 1) amplification
FGFR1 is a receptor-type tyrosine kinase that mediates tumorigenesis through the MAPK and PI3K pathways. 13-25% of squamous lung cancers can be detected with this mutation, which is rare in lung adenocarcinoma.
The prognostic impact of FGFR1 mutations remains unknown, as the reported findings are inconsistent. Studies using FGFR inhibitors to treat squamous lung cancer are just beginning. Data from preliminary studies suggest that treatment of FGFR1-positive squamous lung cancer with BGJ398 (a broad-based FGFR inhibitor) resulted in a response rate of 11.7%.
Mutations in the DDR2 (discogenic death receptor 2) gene
DDR2 is a tyrosine kinase receptor that can only be activated by collagen, not peptide growth factors, and promotes cell migration, proliferation, and survival. DDR2 mutations can occur in 4-5% of lung squamous cell carcinomas. Dasatinib is a tyrosine kinase inhibitor that has been used in chronic granulocytic leukemia. Recent studies have found that dasatinib is effective in treating synchronous chronic granulocytic leukemia in lung squamous carcinoma with DDR2 mutations. And clinical studies of dasatinib for lung squamous carcinoma with DDR2 mutation are still ongoing.
Abnormal PI3K signaling pathway
PI3K signaling pathway is a core pathway for tumor survival and proliferation. amplification of PI3KCA and AKT1 gene functions and loss of PTEN gene functions can cause alterations in PI3K signaling pathway. PI3KCA amplification and mutations have been reported to account for 37% and 9% of non-small cell lung cancers, respectively. PI3KCA mutations are a poor prognostic factor for lung squamous cell carcinoma. PI3KCA inhibitors are not yet available.
Outlook
EGFR and ALK gene testing of tumors is gradually becoming routine, and more testing is urgently needed. The problem now is that sequential testing for multiple genes can lead to inefficiency in this work. A recent study has demonstrated that multiplex testing is in principle feasible. With multiplex testing, mutated genes can be quickly identified and molecularly targeted for lung cancer patients, which can significantly improve survival.
At the same time, new cancer driver genes are being discovered all the time. In a comprehensive genomic study of lung adenocarcinoma, more than 75% of the genetic alterations were found to be targeted. Results from another genomic study of lung squamous cell carcinoma showed that prolonged exposure to oncogenic microenvironments causes cancer, regardless of your ethnicity or where you live.
The latest findings from molecularly targeted studies of non-small cell lung cancer will give patients new hope for treatment. The next genome sequencing will be of close clinical relevance.
While this review only addresses molecularly targeted therapies and associated cancer driver genes, other targeted therapies for non-small cell lung cancer are also thriving. For example, bevacizumab (an anti-angiogenic agent) in combination with paclitaxel + platinum therapy can improve overall survival. Another thriving therapeutic area is molecular modulation of the immune response.
As knowledge of the theory of tumor immunobiology continues to grow, new immunotherapies are being developed at a rapid pace. For example, monoclonal antibodies have been created. These therapies have already demonstrated their power in the treatment of melanoma. Not surprisingly, they will also make their mark in the treatment of non-small cell lung cancer.
Summary
Genetic testing for non-small cell lung cancer has completely changed the way it was staged and treated. NSCLC is no longer considered as one disease, but as a heterogeneous class of diseases composed of different molecular subtypes. The result is that the targeted application of molecularly targeted drugs has improved the clinical outcomes of countless patients. In the field of lung adenocarcinoma, for example, EGFR gene mutations and ALK gene recombination mean that chemotherapy alone is no longer the treatment of choice.
Not long ago, the purpose of a tumor biopsy was simply to diagnose the tumor. Now, however, this has changed. Performing tissue biopsies to determine EGFR and ALK status in patients with non-small cell lung cancer is now an important diagnostic step.
Targeted therapy for advanced non-small cell lung cancer.