There are currently three generations of approved EGFR-TKIs: First-generation (1G) EGFR-TKIs, erlotinib and gefitinib; second-generation (2G) EGFR-TKIs, afatinib and dacomitinib; and third-generation (3G) EGFR-TKIs, osimertinib, aumolertinib, furmonertinib and befotertinib (12).

The quinazoline ring serves as the mother ring structure for both the 1G and 2G EGFR-TKIs (13). The 1G EGFR-TKIs bind to the ATP-binding site of EGFR reversibly and noncovalently, whereas the 2G EGFR-TKIs contain an acrylamide functional group that covalently binds to the ATP-binding domain Cys797 of EGFR for potent and long-lasting irreversible inhibition (13). The parent ring structure of the 3G EGFR-TKIs is 2-aminopyrimidine, and it retains the acrylamide functional group as an irreversible covalent-binding inhibitor (13). The several generations of EGFR-TKIs have different activity ranges due to their structural differences (14). The 1G EGFR-TKIs have the ability to inhibit EGFR-sensitive mutations. The 2G EGFR-TKIs are pan-human epidermal growth factor receptor (HER) inhibitors that cannot only irreversibly covalently inhibit multiple ErbB family receptors, including EGFR, ErbB2 and ErbB4, but also simultaneously inhibit the homodimerization and heterodimerization of HER family receptors, resulting in more potent antitumor activity by completely blocking the HER signaling pathway. The 3G EGFR-TKIs selectively inhibit the EGFR T790M mutation and the EGFR-sensitive mutation.

The Iressa Pan-Asia Study (IPASS) is a phase III RCT that compared the 1G EGFR-TKI gefitinib to carboplatin/paclitaxel chemotherapy in previously untreated never-smokers and light ex-smokers with advanced lung adenocarcinoma (15). The IPASS results demonstrated a notable PFS benefit with gefitinib in patients with NSCLC with the ex21 L858R mutation [hazard ratio (HR), 0.55; 95% confidence interval (CI), 0.35–0.87], but no significant overall survival (OS) benefit was observed (15). Furthermore, the ENSURE study is a phase III RCT that compared first-line erlotinib to gemcitabine/cisplatin in patients with EGFR mutation-positive NSCLC from China, Malaysia and the Philippines. The study demonstrated that PFS, but not OS, was improved with erlotinib vs. gemcitabine + cisplatin chemotherapy. In patients with the 21 L858R mutation, the HR for PFS was 0.57 (95% CI, 0.31–1.05; median PFS, 8.3 vs. 7.1 months), whereas the HR for OS was 1.05 (95% CI, 0.60–1.84; median OS, 25.3 vs. 27.2 months) (16). However, neither the EURTAC (8.4 vs. 6.0 months; HR, 0.55; 95% CI, 0.29–1.02; P=0.054) nor the CONVINCE study (11.1 vs. 7.8 months; HR, 0.76; 95% CI, 0.43–1.33; P=0.331) demonstrated a significant PFS benefit with 1G EGFR-TKIs (17,18). Additionally, the INCREASE study evaluated the efficacy of high-dose icotinib (250 mg, three times/day), another 1G EGFR-TKI for patients with ex21 L858R-mutated. The results revealed a prolonged PFS compared with regular-dose icotinib (125 mg, three times/day; 12.9 vs. 9.2 months; HR, 0.75; 95% CI, 0.53–1.05; P<0.05) (19). The aforementioned results are presented in Table I.

In patients with the ex21 L858R mutation, afatinib demonstrated a marked PFS benefit (HR, 0.32; 95% CI, 0.19–0.52) compared with chemotherapy in the Asian LUX-Lung 6 trial, but not in the global LUX-Lung 3 trial (HR, 0.73; 95% CI, 0.46–1.17), possibly due to differences in the study population or the efficacy of the chemotherapy comparators used in each study (20,21). However, neither of the two trials demonstrated a significant improvement in OS with first-line afatinib vs. chemotherapy for ex21 L858R (20–22). Afatinib was compared with gefitinib in the LUX-Lung 7 trial, and neither PFS (10.9 vs. 10.8 months; HR, 0.71; 95% CI, 0.48–1.06) nor OS benefit (25.0 vs. 21.2 months; HR, 0.91; 95% CI, 0.62–1.36) was observed in patients with the ex21 L858R mutation (23,24). In line with this finding, Lau et al (25) reported no significant improvement in OS for patients with the ex21 L858R mutation when they compared afatinib to gefitinib and erlotinib in a real-world study (median OS, 25.4 vs. 20.6 months).

In comparison, the encouraging results of dacomitinib, another 2G EGFR-TKI, warrant special attention. Notably, the ARCHER 1050 trial reported that dacomitinib outperformed gefitinib in terms of both PFS (12.3 vs. 9.8 months; HR, 0.63; 95% CI, 0.44–0.88) and OS (32.5 vs. 23.2 months; HR, 0.67; 95% CI, 0.47–0.94) in patients with the ex21 L858R mutation (26–28). According to a sub-analysis of ARCHER 1050, first-line dacomitinib was markedly associated with prolongation of PFS and improved OS compared with gefitinib in patients from Asian populations with the ex21 L858R mutation: The mean PFS for dacomitinib compared with gefitinib was 16.0 vs. 11.1 months, with an HR of 0.505 (95% CI, 0.337–0.758; P=0.0004), and the median OS was 36.5 months vs. 25.6 months, with an HR of 0.622 (95% CI, 0.415–0.931; P=0.01) (29). In another sub-analysis, improvements in PFS and OS with dacomitinib over gefitinib were observed in patients with dacomitinib dose reduction in the ex21 L858R mutation subgroup. Dacomitinib dose reduction improved PFS and OS in 67 and 68% of patients with ex21 L858R, respectively, making dacomitinib the first TKI to demonstrate improved PFS and OS over gefitinib in patients with dose reduction in the ex21 L858R subgroup (30).

Consistent real-world data report the benefits of dacomitinib in the ex21 L858R population, as demonstrated in ARCHER1050. In a multicenter retrospective analysis (TOPGAN2020-02), patients from nine Japanese institutions who received dacomitinib for advanced EGFR-mutant NSCLC that had progressed after EGFR-TKI treatment were included. Subset analysis indicated that patients with the ex21 L858R mutation had a longer PFS than those with ex19del (median PFS, 5.8 vs. 4.1 months; P=0.018) (31). In another real-world study in China, first-line dacomitinib treatment demonstrated a promising efficacy (median PFS, 16.3 months) and tolerable adverse events (AEs) among patients with NSCLC with the EGFR ex21 L858R mutation (32). The initial dose and baseline brain metastasis status did not have a significant impact on the PFS among these patients (32). ARIA is a noninterventional study of the real-world utilization of dacomitinib and the associated clinical outcomes in patients from Asian populations with advanced EGFR mutation-positive NSCLC (33). Its recent interim analysis reported that at data cutoff, the median real-world PFS was longer in patients with the ex21 L858R mutation than in those with ex19del (30.5 vs. 20.3 months) (33). The aforementioned results are presented in Table I.

The acquired T790M mutation has been reported in 36.5% of patients with ex21 L858R after 1G or 2G TKI treatment (34). The 3G EGFR-TKIs are irreversible inhibitors that were developed to overcome the increased ATP and EGFR affinity caused by the T790M mutation (35). In the FLAURA study, patients with the ex21 L858R mutation who received osimertinib experienced a significant improvement in PFS (14.4 vs. 9.5 months; HR, 0.51; 95% CI, 0.36–0.71; P<0.001) but not OS (HR, 1.00; 95% CI, 0.71–1.40) compared with those treated with the 1G EGFR-TKI gefitinib or erlotinib (36,37). In the phase III trial AENEAS (NCT03849768), the median PFS for the aumolertinib and gefitinib groups was 13.4 and 8.3 months, respectively (HR, 0.60; 95% CI, 0.40–0.89; P=0.0102) (38). The 12-month OS rates for aumolertinib and gefitinib were similar, at 86.2% (95% CI, 80.8–90.2) and 85.3% (95% CI, 79.8–89.4), respectively. Additionally, the real-world research OSI-FACT retrospectively assessed osimertinib as a first-line treatment for EGFR-mutant NSCLC. In terms of mutation types, the median PFS for those with the ex21 L858R mutation was 16.9 months (95% CI, 13.6-not reported), demonstrating a comparable level of disease control to that observed in clinical trials (39). However, the superiority of osimertinib over the 2G EGFR-TKIs remains unknown in the real world. Ito et al (40) evaluated patients with NSCLC treated with osimertinib or afatinib as the first-line therapy at 15 Japanese institutions between May 2016 and October 2019. The survival curves for patients with ex21 L858R indicated that afatinib tended to provide an improved survival benefit than osimertinib. Additionally, there were marked differences in PFS and OS between the two treatments for patients with ex21 L858R without brain metastases, with HRs favoring afatinib (40). In another Dutch nationwide real-world cohort, Gijtenbeek et al (41) confirmed that the OS benefit for patients with ex21 L858R treated with osimertinib as the first-line therapy was not superior to that of 1G and 2G TKIs. The aforementioned results are presented in Table I.

The 4G EGFR-TKIs have been developed for targeting the osimertinib-resistant mutations T790M and C797S. In preclinical and/or phase I studies, a number of 4G EGFR-TKIs, including BLU-945, EAIO45, JIN-A02 and BBT176, have demonstrated inhibitory activities for classical EGFR mutations as well as T790M + C797S (42–44). Additional 4G TKI therapeutic data for ex21 L858R is expected in the future.

Rash, diarrhea, paronychia, oral mucositis, hepatotoxicity and interstitial lung disease are among the most common AEs associated with EGFR-TKIs, with different generations of EGFR-TKIs having different safety profiles (45,46). As 1G EGFR-TKIs are associated with an increased risk of hepatotoxicity and interstitial lung disease, they should be used with caution in patients with liver disease (45,46). Meanwhile, 2G TKIs are associated with common and tolerable AEs such as dermatitis, diarrhea and oral mucositis (47). Furthermore, 3G TKIs have a reduced prevalence of typical AEs such as rash and diarrhea, but they are coupled with a higher risk of cardiotoxicity (48). As a result, patients with pre-existing heart problems should use them with caution.

Comparison of the safety of different generations of EGFR-TKIs is undefined in the general study population that includes both patients with ex19del and ex21 L858R. In LUX-Lung 7, the frequency of grade ≥3 AEs was reported to be similar in patients receiving afatinib or gefitinib (57% vs. 52%) (23). However, grade ≥3 treatment-related AEs (TRAEs) were reported in 63% of patients given dacomitinib and in 41% of patients given gefitinib in ARCHER 1050 (26). In FLAURA, AEs of grade 3 or higher were less frequent in patients treated with osimertinib than with gefitinib or erlotinib (34% vs. 45%) (36), whilst patients in the aumolertinib and gefitinib groups experienced comparable grade ≥3 AEs in AENEAS (36.4% vs. 35.8%) (38). By contrast, patients who received EGFR-TKIs had apparently fewer grade ≥3 AEs than those who received chemotherapy, with 28.7% vs. 61.0% in IPASS (49), 9.5% vs. 24.8% in CONVINCE (18), 35.5% vs. 57.7% in ENSURE (16), 45% vs. 67% in EURTAC (17), 49% vs. 48% in LUX-Lung 3 (20), 36.0% vs. 60.2% in LUX-Lung 6 (21) and 23% vs. 47% in AURA3 (50). INCREASE is the only trial that reported safety evaluations in different mutation subpopulations: Patients in the L858R-high-dose group experienced notably more TRAEs (81%) than those in the L858R-reduced-dose group (55%) and ex19del-reduced-dose group (66%), whereas the incidences of grade 3/4 TRAEs were similar across all groups (19). Nevertheless, the potential for safety differences between EGFR mutation subgroups warrants further investigation.

Whilst the PFS benefits of 3G TKIs outperform those of 1G and 2G TKIs, only 2G dacomitinib has demonstrated OS benefits, and 3G TKI OS data remain unmatured. Certain preclinical evidence may explain the possible reason for the efficacy of dacomitinib in ex21 L858R NSCLC. An in-vitro study reported that dacomitinib can effectively inhibit EGFR phosphorylation, particularly hyperphosphorylation at the Y845 site, which is one of the reasons for the low sensitivity of the ex21 L858R mutation to TKIs (51). Another in-vitro study reported that dacomitinib had a sustained inhibitory effect on EGFR in cells expressing the ex21 L858R mutation for ≤30 min after drug withdrawal, whereas the inhibitory effect of the 1G and 3G TKIs vanished immediately (52). Additionally, the half-maximal inhibitory concentration value of 2G TKIs (2.6–4 nM) was much lower than that of 1G TKIs (16–26 nM) and the 3G TKI osimertinib (9 nM), especially for dacomitinib, indicating another explanation that dacomitinib has a stronger inhibitory effect on the ex21 L858R mutation than other TKIs (53). These preliminary findings support the use of dacomitinib in the treatment of ex21 L858R NSCLC.

Furthermore, studies have reported that sequential 3G TKIs following initial 2G TKI treatment may also result in long OS benefits. The ARCHER1050 study reported that the median OS of patients with the ex21 L858R mutation who were resistant to first-line dacomitinib therapy followed by osimertinib was 44.7 months, demonstrating the survival benefit of 2G sequential 3G TKI therapy (30). In addition, two previous noninterventional trials, GioTag (NCT03370770) and UpSwinG (NCT04179890), reported notable OS results in patients who received sequential afatinib/osimertinib. The GioTag observational study evaluated the role of sequential osimertinib after afatinib failure in patients with ex21 L858R mutations, reporting an OS of 33.0 (29.8–37.0) months for these patients (54). In the global study UpSwinG, first-line afatinib and second-line osimertinib resulted in a median OS of 33.1 (24.9–41.8) months in patients with the ex21 L858R mutation in regular clinical practice (55). Moreover, Miura et al (56) performed a combined analysis of patients from Asian populations from both studies, and the results indicated a median OS of 39.1 (29.3–48.5) months in patients with the ex21 L858R mutation. More research comparing first-line 3G EGFR-TKIs to sequential therapy for patients with NSCLC with the ex21 L858R mutation is expected (57,58).

Combination therapy is currently a common treatment option for NSCLC with EGFR mutations. Combining EGFR-TKIs with antiangiogenic therapy (T+A) or chemotherapy (T+C) can produce synergistic antitumor effects via several potential molecular mechanisms. By activating caspase-7, the combination of EGFR-TKIs and chemotherapy enhances apoptotic signaling, significantly inhibiting cell growth, promoting cell death and preventing resistance mediated by epithelial-mesenchymal transition (59,60). Additionally, antiangiogenic agents can normalize the vascular wall and network structure, enhancing the delivery and penetration of EGFR-TKIs into tumor tissues (61). EGFR is also expressed on tumor-associated endothelial cells, and its inhibition by EGFR-TKIs in combination with antiangiogenic agents can suppress tumor angiogenesis synergistically (62). Furthermore, antiangiogenic therapy can prevent compensatory increases in angiogenesis from both tumor and stromal sources caused by EGFR-TKIs (63).

Several studies have assessed the clinical efficacy of combining EGFR-TKIs and chemotherapy for patients with EGFR mutations, and combination therapy shows clinical benefits compared with EGFR-TKI monotherapy. A significant PFS benefit was demonstrated for patients with L858R receiving combination therapy compared with patients receiving gefitinib in the JMIT trial (median PFS, 12.6 vs. 10.9 months; HR, 0.58; 95% CI, 0.33–1.01; P=0.054), NCT02148380 trial (HR, 0.31; 95% CI, 0.15–0.66) and NEJ009 trial (HR, 0.55; 95% CI, 0.38–0.80) (64–67). As presented at the 2023 World Conference on Lung Cancer, in FLAURA2, osimertinib in combination with chemotherapy demonstrated a marked PFS improvement compared with osimertinib alone for patients with the L858R mutation (median PFS, 24.7 vs. 13.9 months; HR, 0.63; 95% CI, 0.44–0.90), with a benefit degree similar to that of the ex19del subgroup (68). In addition, Yan et al (69) retrospectively analyzed 76 patients with NSCLC with EGFR mutations who received EGFR-TKI monotherapy (gefitinib, erlotinib or icotinib) or in combination with a platinum-based regimen (cisplatin or carboplatin + paclitaxel, docetaxel, pemetrexed or gemcitabine). The results demonstrated that the PFS and OS of patients with L858R in the combination group were significantly longer than in the monotherapy group (median PFS, 7.2 vs. 5.8 months; P=0.013; and median OS, 22.0 vs. 18.7 months; P=0.024). The aforementioned results are presented in Table II.

The combination of EGFR-TKIs and antiangiogenic drugs has also shown efficacy in first-line treatment for patients with advanced EGFR-mutated NSCLC. A total of four clinical trials assessed the prognosis of the combination of erlotinib and bevacizumab compared with erlotinib, including the CTONG1509 trial, NEJ026 trial, JO25567 trial and a phase II trial in Japan. Moreover, NCT03126799 and the RELAY study evaluated the efficacy and safety of the combination of erlotinib and ramucirumab compared with erlotinib, and CTONG1706 was performed to compare apatinib + gefitinib with gefitinib monotherapy (70–75). For patients with the L858R mutation, a significant PFS benefit of combined therapy was demonstrated in the CTONG1509 trial (median PFS, 19.5 vs. 9.7 months; HR, 0.50; 95% CI. 0.32–0.77; P=0.001), NEJ026 trial (median PFS, 17.4 vs. 13.7 months; HR, 0.57; 95% CI. 0.33–0.97), RELAY trial (median PFS, 19.4 vs. 11.2 months; HR, 0.62; 95% CI, 0.44–0.87; P=0.006) and RELAY Japanese Subset (median PFS, 19.4 vs. 10.9 months; HR, 0.51; 95% CI, 0.32–0.84; P=0.006) (70–72,76). However, no significant OS benefit was demonstrated for the ex21 L858R mutation in these ongoing trials (70–72). Moreover, PFS benefits were not revealed to be significant in the exon 21 L858R subgroup in the JO25567 trial (median PFS, 13.9 vs. 7.1 months; HR, 0.67; 95% CI, 0.38–1.18; P=0.1653), CTONG1706 (median PFS, 11.9 vs. 10.1 months; HR, 0.72; 95% CI, 0.48–1.09; P=0.123) and NCT03126799 (HR, 0.63; 95% CI. 0.35–1.13; P=0.118) (73–75). The aforementioned results are presented in Table II.

In the general population, the safety profiles of EGFR-TKI combination therapy were consistent with the known profiles of both drugs, including liver dysfunction, neutropenia, fatigue, hematologic toxicities and skin rash. The safety findings in several studies are constant in that combined therapy has more AEs than monotherapy. For T+C trials, the proportion of grade ≥3 treatment-emergent AEs (TEAEs) was notably higher in the gefitinib + chemotherapy group than in the gefitinib group in both the JMIT study (42% vs. 19%) (64) and the NEJ009 study (65.3% vs. 31.0%) (66). Similarly, for the T+A regimen, patients receiving erlotinib + bevacizumab or ramucirumab experienced more grade ≥3 TEAEs than patients in the erlotinib-only group, with 54.8% vs. 26.1% in CTONG1509 (70), 88% vs. 46% in NEJ026 (71), 72% vs. 54% in RELAY (72), 91% vs. 53% in JO25567 (73) and 50.6% vs. 20.6% in NCC2016-0107 (75). Notably, in CTONG1706, grade ≥3 TEAEs were also reported more frequently in the apatinib + gefitinib group than in the gefitinib monotherapy group (84.1% vs. 37.7%) (74). However, no data on the safety differences between EGFR mutation subgroups have been published, to the best of our knowledge.

In general, studies have reported that both T+A and T+C combination therapies had improved PFS for patients with L858R compared with EGFR-TKI monotherapy (64–75). However, it is unknown whether monotherapy or combination therapy is a more effective first-line treatment for these patients in terms of OS benefits. Amivantamab is an EGFR- and mesenchymal-epithelial transition-bispecific antibody with immune cell-directing activity (33). The phase III trial MARIPOSA (NCT04487080) compared amivantamab + lazertinib, a central nervous system-penetrating 3G EGFR-TKI, to osimertinib in the first-line setting. Its early PFS data demonstrated that amivantamab + lazertinib outperformed osimertinib in patients with the ex21 L858R mutation (HR, 0.78; 95% CI, 0.59–1.02) or ex19del (HR, 0.65; 95% CI, 0.51–0.85) after a median follow-up of 22.0 months (33). Future studies combining EGFR-TKIs with treatments other than chemotherapy and antiangiogenic therapy deserve attention.

Additionally, despite their effectiveness in extending survival benefits, the combination of other treatments with EGFR-TKIs may result in additional AEs. A meta-analysis by Qi et al (77) revealed that compared with osimertinib, the combination of 1G T+A (HR, 2.40; 95% CI, 1.70–3.40) and 1G T+C (HR, 2.50; 95% CI, 1.60–4.60) significantly increased the risk of grade 3 or worse AEs, with the following risk rank: osimertinib < 1G EGFR-TKIs < 2G EGFR-TKIs < 1G T+A < 1G T+C. As a result, when prescribing combination treatments, clinicians should be more cautious about the increased toxicities as well as the toxicity profile of each treatment for clinical decision making and improved management.

Furthermore, regimens combining EGFR TKIs with additional EGFR-targeting therapies have been assessed to delay/prevent resistance and to achieve more intense suppression. For example, studies have begun to investigate combination therapy with EGFR TKIs and EGFR monoclonal antibodies (mAbs) due to their synergistic antitumor effects: EGFR mAbs inhibit ligand-induced activation of TKD by blocking ligand-EGFR binding extracellularly, whilst EGFR TKIs reduce the relative affinity of TKD for ATP intracellularly (78–80). This ‘sandwich’ strategy also enables a decreased dosage of each medication, facilitating the management of adverse effects without compromising the therapeutic efficacy. Preclinical data indicate that the afatinib-based ‘sandwich’ method notably delays drug resistance in transgenic mice carrying tumors with the EGFR L858R mutation (78). However, the phase II RCT SWOG S1403 reported that adding cetuximab to afatinib did not enhance outcomes in patients with NSCLC with classic mutations (exon 19del and exon 21 L858R), with 30% of patients discontinuing cetuximab due to intolerable AEs (79). Using comprehensive pharmacology profiling and molecular docking analyses, a recent study identified EGFR as a potential target of the key therapeutic component of Spirulina, suggesting that small molecules acting through several mechanisms to EGFR may be used as adjuvants to enhance the treatment effectiveness or sensitivities of EGFR TKIs (80).