Superior clinical outcomes in patients with non-small cell lung cancer harboring multiple ALK fusions treated with tyrosine kinase inhibitors

Introduction

Lung cancer is one of the most frequently diagnosed cancers and the leading cause of cancer-related mortality worldwide, with non-small cell lung cancer (NSCLC) accounting for approximately 85% of all diagnosed cases (1). Approximately 3–5% of NSCLC is driven by gene rearrangements in anaplastic lymphoma kinase (ALK) (1). Echinoderm microtubule-associated protein-like 4 (EML4) is the most common ALK fusion partner and is also referred to as canonical ALK fusion (2). To date, at least 15 different EML4-ALK fusion variants have been discovered, with variant 1 and variant 3 being the most common variants (3-5). Other noncanonical ALK fusions, such as SLMAP-ALK, CMTR1-ALK, SDK1-ALK, HIVEP1-ALK, and STRN-ALK, have been reported in patients with NSCLC, but their large-scale clinical data are still immature (6-11).

Crizotinib was the first tyrosine kinase inhibitor (TKI) to be approved by the US Food and Drug Administration for patients with ALK-rearranged NSCLC (12), and its efficacy is superior to standard chemotherapy, which has a significant longer progression-free survival (PFS), whether in previously treated ALK-positive NSCLC or previously untreated ALK-positive NSCLC patients (13,14). Moreover, second-generation ALK-TKIs, such as alectinib and ceritinib, have been developed for patients with ALK-positive NSCLC and have a higher potency compared to crizotinib (15-17). Patients with ALK fusion NSCLC have been effectively treated with ALK-TKIs, and the therapeutic outcome for canonical EML4-ALK fusion has been widely studied, including the efficacy on different EML4-ALK variants (18-20). Different ALK fusion variants might be associated with the development of resistance mutations and might be an important factor for the selection of ALK-TKIs (21,22). For patients with ALK rearrangements, more than one aberration in the ALK gene might be involved. A few case reports have described multiple ALK fusions, with some of these indicating that patients with NSCLC and multiple ALK fusions show a sensitivity to crizotinib or alectinib (23-25). However, few studies have analyzed the prognosis in patients with NSCLC and multiple ALK fusions, and data on efficacy of ALK-TKIs in this setting is currently lacking. Zhang et al. found that patients with dual ALK fusion partners have a significantly shorter median PFS than do single ALK fusion partners (26). However, Kang et al. found that complex ALK fusions are associated with a better prognosis in patients with advanced NSCLC (27). In the present study, we aimed to analyze the therapeutic outcome in patients with NSCLC and multiple ALK fusions who received ALK-TKIs to provide a reference for the treatment of this patient group. We present this article in accordance with the STROBE reporting checklist (available at https://tlcr.amegroups.com/article/view/10.21037/tlcr-23-484/rc).

Methods

Patients and methods

We retrospectively evaluated 2,231 patients with NSCLC who underwent next-generation sequencing (NGS) from 2016 to 2020 at West China Hospital. A total of 125 ALK-positive patients were included in the analysis. In this study, a cohort of 125 patients was established, all of whom were pathologically confirmed to have NSCLC and identified to harbor ALK rearrangements using NGS.

Out of the initial cohort, a subset of 56 patients who received ALK-TKIs for locally advanced or metastatic NSCLC were selected for further prognostic analysis. Inclusion criteria for this subgroup were: (I) the presence of advanced or metastatic NSCLC; (II) confirmed ALK-rearranged status; (III) treatment with ALK-TKIs as first- or second-line monotherapy; and (IV) availability of complete prognostic data. Patients were excluded from the subgroup analysis if they met any of the following criteria: (I) did not receive any treatment; (II) received only chemotherapy; (III) underwent surgery and/or postoperative maintenance treatment; (IV) were treated with a combination of ALK-TKIs and chemotherapy or bevacizumab; (V) received only immunotherapy; or (VI) were lost to follow-up within 1 month of initiating ALK-TKIs treatment. This study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by the Ethics Committee of West China Hospital of Sichuan University (No. 2022-1085), and individual consent for this retrospective analysis was waived.

To supplement our in-house data, we conducted a comprehensive literature search of PubMed and Embase for additional case reports. Our search, which spanned until March 30, 2023, included case studies involving patients with NSCLC exhibiting multiple ALK fusions who had undergone ALK-TKIs treatment. Our search strategy utilized key terms such as “ALK double fusions”, “coexistence/coexisting ALK fusion”, “multiple ALK fusions”, “complex ALK fusions”, “triple ALK fusions”, “dual ALK fusions”, and “nonreciprocal/reciprocal ALK fusion”. The studies selected from this search were required to meet the following criteria: (I) involve patients with advanced or metastatic NSCLC; (II) confirm the presence of multiple ALK fusions; (III) detail treatment with ALK-TKIs; and (IV) provide available PFS data. Our search yielded 23 potential cases. However, 17 of these were excluded due to a lack of necessary prognostic data (n=12), the administration of only postoperative maintenance treatment (n=3), or treatment with epidermal growth factor receptor (EGFR) TKIs (n=2) (Figure S1). This left us with 6 relevant cases from the literature of patients with NSCLC and multiple ALK fusions.

Consequently, a total of 62 patients with NSCLC and multiple ALK fusions who received ALK-TKIs treatment were analyzed in our study. This included 56 patients from our own data and an additional 6 from the literature.

NGS

Genomic DNA of NSCLC formalin-fixed, paraffin-embedded (FFPE) specimens was purified using a QIAamp DNA FFPE tissue kit (Qiagen, Hilden, Germany). Quantification of DNA obtained from FFPE tissues was assessed using a Qubit 2.0 fluorimeter with a double-stranded DNA high-sensitivity assay kit (Life Technologies, Thermo Fisher Scientific, Waltham, MA, USA). DNA was profiled with a panel targeting 56 lung cancer-associated genes (Burning Rock Biotech, Guangzhou, China). Sequence data were mapped to the human genome hg19 using Burrows-Wheeler Aligner software (version 0.7.10). Genome Analysis Toolkit GATK 3.2 software (RRID:SCR_001876; Broad Institute, Cambridge, MA, USA) was used for local alignment optimization. Variant calling was performed with MuTect software (Broad Institute).

Measurement of clinical outcomes

Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1 was used to assess the response. The objective response rate (ORR) includes complete response (CR) and partial response (PR). The disease control rate (DCR) includes CR, PR, and stable disease (SD). PFS was measured from the date of initiation of ALK-TKI treatment until disease progression or death. Overall survival (OS) was calculated from the date of initiation of ALK-TKIs to death due to any causes or at the last follow-up time. The primary clinical outcomes were PFS and OS. The secondary clinical outcomes were ORR and DCR. For patients included from the literature search, the prognosis data were known.

Definition of multiple ALK fusions and single ALK fusion

In our retrospective study, multiple ALK fusions were defined as more than 1 (≥2) ALK fusion in patients with NSCLC, and a single ALK fusion was defined as only 1 ALK fusion, including a noncanonical ALK fusion, being detected.

Statistical analysis

The comparison of clinical characteristics between different ALK fusion groups was performed using the Fisher exact test. For survival data, Kaplan-Meier curves were analyzed using the log-rank test. Univariate and multivariate analyses were performed using the Cox regression model. All statistical analyses were conducted with SPSS (version 26; IBM Corp., Armonk, NY, USA) and R software (version 4.0.3 or version 4.2.2; The R Foundation for Statistical Computing, Vienna, Austria). Two-sided P values of less than 0.05 were considered statistically significant.

Results

ALK fusions identified in 125 patients with NSCLC

Among 2,231 patients with NSCLC who underwent NGS, ALK fusion was detected in 125 (125/2,231, 5.6%). We summarized the distribution of the ALK fusions in Table S1. Among the 125 ALK-positive patients, most (82/125, 65.6%) had single EML4-ALK fusion, in whom EML4-ALK variant 1 and EML4-ALK variant 3 were the most common EML4-ALK fusion; meanwhile, 17 (17/125, 13.6%) had single non-EML4-ALK fusion, 4 (4/17, 23.5%) of whom had an intergenic sequence ALK fusion, including CENPA-ALK (Cintergenic:A20), CHRNA7-ALK (Cintergenic:A20), MEMO1-ALK (Mintergenic:A20), and PDCL3-ALK (Pintergenic:A20). Except for a single ALK rearrangement, 26 (20.8%) had multiple ALK fusions, 23 patients harbored 2 coexisting fusions, and 3 had 3 coexisting fusions. Among these patients with multiple ALK fusions, 22 (22/26, 84.6%) had EML4-ALK fusion, and most had coexisting EML4-ALK variant 1 (8/26, 30.8%) or EML4-ALK variant 3 (9/26, 34.6%). Moreover, 22 (22/26, 84.6%) of these patients had a 3'-ALK fusion, and only 4 patients had both a 3'-ALK fusion and 5'-ALK fusion (Table S1).

Clinical characteristics and the ALK fusion distribution in 62 patients who received ALK-TKIs treatment

Among the 62 patients with NSCLC harboring an ALK fusion treated with ALK-TKIs (Table 1), the median age was 50.4 years, 44 patients had a single ALK fusion, and the remaining 18 patients had multiple ALK fusions. In the single ALK fusion group, 8 (8/44, 18.2%) patients received alectinib, 34 (34/44, 77.3%) received crizotinib, and the remaining 2 patients received ensartinib and ceritinib, respectively. In the multiple ALK fusion group, 8 patients (8/18, 44.4%) accepted alectinib, and the remaining 10 (10/18, 55.6%) patients received crizotinib. The baseline characteristics between the multiple ALK fusion and single ALK fusion groups were compared, and no significant differences were observed in the baseline characteristics in these two groups except for contralateral lung metastasis (P=0.025) (Table 1).

We further analyzed the distribution of ALK fusions in 62 patients with NSCLC who received ALK-TKIs (Figure 1). Among these 62 patients, 71.0% (44/62) had a single ALK fusion, and among these patients, the most common ALK fusion was still EML4-ALK (36/44, 81.8%), and 8 patients (8/44, 18.2%), had a non-EML4-ALK fusion. The remaining 18 (18/62, 29.0%) patients had multiple ALK fusions, 6 of whom were included through literature retrieval (Figure 1).

Figure 1 Distribution of ALK fusions in 62 patients who received ALK-TKIs. (A) ALK fusions were subdivided into multiple ALK fusions and single ALK fusion. (B) The frequency of EML4-ALK fusion and non-EML4-ALK fusion in single ALK fusion patients. (C) ALK fusion information in 18 patients. ALK, anaplastic lymphoma kinase; TKI, tyrosine kinase inhibitor; EML4, echinoderm microtubule-associated protein-like 4.

Better prognosis in patients with NSCLC with multiple ALK fusions who received ALK-TKIs and subgroup analysis

Considering the lack of a standardized prognosis for NSCLC patients harboring multiple ALK fusions who undergo ALK-TKIs treatment, we initiated this study to discern whether these patients exhibit a superior or inferior prognosis compared to NSCLC patients harboring a solitary ALK fusion. We analyzed the response data of the different groups, and there was no significantly higher ORR or DCR between the single ALK fusion group and the multiple ALK fusion group, with P values of P=0.121 and P=1.000, respectively (Figure 2A,2B). Moreover, the median PFS was significantly increased in the patients with multiple ALK fusions (26.9 months) compared to those with a single ALK fusion (11.2 months, P=0.009; Figure 3). For OS, as shown in Figure 4, the multiple ALK fusion group tended to have a better OS than did the single ALK fusion group [hazard ratio (HR) =0.428; 95% confidence interval (CI): 0.095–1.928], although the P value was not statistically significant (P=0.26). In subgroup analyses of PFS, irrespective of age, gender, smoking status, types of TKIs drug, and treatment lines, the magnitude of the treatment effect was generally consistent across patients generally (Figure 5), but the magnitude of benefit was lower in the subgroup of patients receiving second generation ALK-TKIs therapy. Similar results were seen in the subgroup analyses of OS, but only a small number of patients had complete OS data (Figure 6).

Figure 2 Different clinical outcomes in multiple ALK fusion group and single ALK fusion group. (A) Histogram showing the proportions of patients who achieved an ORR in the multiple ALK fusion group and single ALK fusion group. (B) Histogram showing the proportions of patients with controlled disease in the multiple ALK fusion group and single ALK fusion group. ORR, objective response rate; CR, complete response; PR, partial response; SD, stable disease; PD, progressive disease; ALK, anaplastic lymphoma kinase; DCR, disease control rate.

Figure 3 Clinical outcome in the different ALK fusion groups. Kaplan-Meier curve of PFS of ALK-TKI treatment in 62 patients. ALK, anaplastic lymphoma kinase; PFS, progression-free survival; TKI, tyrosine kinase inhibitor.

Figure 4 Clinical outcome in the different ALK fusion groups. Kaplan-Meier curve of OS of ALK-TKI treatment in 62 patients. ALK, anaplastic lymphoma kinase; OS, overall survival; TKI, tyrosine kinase inhibitor.

Figure 5 Univariate analyses of PFS in patients with NSCLC who received ALK-TKIs. ALK, anaplastic lymphoma kinase; HR, hazard ratio; CI, confidence interval; ECOG, Eastern Cooperative Oncology Group; PS, performance status; TKI, tyrosine kinase inhibitor; PFS, progression-free survival; NSCLC, non-small cell lung cancer.

Figure 6 Univariate analyses of OS in patients with NSCLC who received ALK-TKIs. ALK, anaplastic lymphoma kinase; HR, hazard ratio; CI, confidence interval; ECOG, Eastern Cooperative Oncology Group; PS, performance status; TKI, tyrosine kinase inhibitor; OS, overall survival; NSCLC, non-small cell lung cancer.

Multiple ALK fusions was a predictive marker in patients with NSCLC treated with ALK-TKIs

Univariate Cox regression analysis of PFS revealed that ALK-TKIs and ALK fusion had prognostic value, with P values of P=0.004 and P=0.012, respectively (Table S2). We then conducted multivariate Cox regression analysis of PFS, and found that presence of multiple ALK fusions had the potential to serve as a predictive marker of better PFS for patients with ALK-rearranged NSCLC treated with ALK-TKIs (HR =0.490; 95% CI: 0.229–1.049) (Table S2). Due to the prognostic influence of the second-generation ALK-TKIs, to further demonstrate the predictive effect of multiple ALK fusions, we performed subgroup analysis in patients received different ALK-TKIs. Neither receiving first-generation or second-generation ALK-TKIs, patients who harbored multiple ALK fusions had a favorable PFS or OS than those harboring single ALK fusion, although there were no statistically significant differences in patients who received second-generation ALK-TKIs (Figure S2).

To reduce the data bias, we further analyzed the 56 patients came from our hospital. As shown in Table S3, no significant differences were observed in the baseline characteristics in these two groups. Univariate and multivariate Cox regression analyses of PFS revealed similar predictive value of multiple ALK fusions, although the P value was not statistically significant (P=0.091) (Table S4).

Prognosis in ALK-positive patients with brain metastases

In the present study, we investigated the incidence of brain metastases in patients with NSCLC harboring ALK fusion at baseline and analyzed the prognosis of patients with and without metastases: 22.7% (10/44) of single ALK fusion patients had brain metastases while 22.2% (4/18) of multiple ALK fusion patients had brain metastases (Table 1). Among the patients with brain metastases, there was no significant difference in PFS between the single ALK fusion group and multiple ALK fusion group (11.0 vs. 26.9 months, P=0.17) (Figure S3A), and there was also no significant difference in OS between these two groups (P=0.15) (Figure S3B). Moreover, for patients without brain metastases, we found a significantly better PFS in the multiple ALK fusion group (26.0 vs. 15.6 months, P=0.028) (Figure S3C), but no significant difference in OS was reported between these two groups (P=0.76) (Figure S3D).

Discussion

In this retrospective study, we investigated the incidence of multiple ALK fusions in patients with NSCLC harboring ALK rearrangement and analyzed the therapeutic outcome in different ALK fusion groups who received ALK-TKIs. We found that approximately 20% of patients with NSCLC and ALK rearrangement had multiple ALK fusions, and in comparison to the single ALK fusion group, the multiple ALK fusion group had a better response to ALK-TKIs.

An increasing number of cases of complex ALK fusions or coexisting ALK fusions have been reported. Moreover, with the widespread use of NGS, some new ALK rearrangements have been detected. In this retrospective study, we investigated the distribution of ALK fusions in a large Chinese NSCLC cohort. We identified that the most common ALK fusion was EML4-ALK, and among the single EML4-ALK fusions, variant 3 and variant 1 were the most frequently occurring; meanwhile, 13.6% (17/125) had non-EML4-ALK fusion alone, and 20.8% (26/125) had multiple ALK fusions. Previous work has reported a frequency of 79.78% for EML4-ALK fusions and 20.22% (18/89) for non-EML4-ALK fusions, with 17.98% (16/89) showing more than 1 ALK rearrangement (28). Another study reported that 69.3% (104/150) had a single EML4-ALK rearrangement, 12.0% (18/150) had a non-EML4-ALK rearrangement alone, and 18.7% (28/150) had nonreciprocal/reciprocal ALK rearrangements (29). Possible reasons for the observed inconsistency in frequency may include variations in cohort size and the employment of diverse detection tools. ALK-TKIs have dramatically expanded the therapeutic landscape of ALK-positive NSCLC. For patients with NSCLC and multiple ALK fusions, there is no consensus concerning the treatment outcome of these patients. For patients with ALK fusions who received first-line crizotinib, a previous study found that patients with nonreciprocal/reciprocal ALK fusions had a poor prognosis compared to patients with 3'-ALK fusion alone or EML4-ALK fusion alone (29). However, some studies have reported different results. In their study, Kang et al. discovered that patients with NSCLC harboring complex ALK fusions exhibited a more favorable OS compared to those with either pure canonical EML4-ALK fusion or pure noncanonical ALK fusion (27). Xia et al. identified a prolonged yet statistically insignificant difference in PFS between patients with canonical ALK fusions and those with complex ALK fusions (30). In contrast, our study demonstrated that patients with multiple ALK fusions presented with a superior PFS than those with a single ALK fusion. The discrepant therapeutic outcomes in these clinical studies may be due to the different inclusion criteria of multiple ALK fusions and concomitant mutation status. The definition of multiple ALK fusions in our study were more extensive in comparison to those of the nonreciprocal/reciprocal ALK fusion, which was defined as harboring concurrent ALK fusions with at least one 3'-ALK fusion and one 5'-ALK fusion. A different study suggested that concurrent 5'-ALK fusion is associated with poor prognosis (29). Regarding the influence of concomitant mutation on prognosis, one study found that concomitant TP53 or PIK3R2 alteration was predictive of poor survival (31), which was associated with poor prognosis in ALK-rearranged patients. In our present study, the mutation status was not included in analyses because of a lack of complete mutation data. Moreover, in our study, we further demonstrated the superior clinical outcome in patients with NSCLC and multiple ALK fusions, and further confirmed that multiple ALK fusions have the potential to be an independent predictive marker of better PFS in patients with NSCLC treated with ALK-TKIs. For ALK-rearranged NSCLC, genomic heterogeneity has been demonstrated, and which could account for differences in treatment response with ALK-TKIs (32). Among multiple ALK fusions, there are higher rates for the intergenic sequence-ALK and non-EML4-ALK fusions in patients (28), and most have one EML4-ALK fusion, and the other ALK fusion could be a promising target for subsequent ALK-TKIs treatment (27). Zhang et al. found that patients harboring dual ALK fusions with concurrent 5'-ALK fusions had a poor response to ALK-TKIs targeted therapy, and then also identified that specific combinations of ALK fusions in multiple ALK fusions bring about different treatment responses (29). In our study, there were only 3 patients harboring multiple ALK fusions with concurrent 5'-ALK fusions, and most of them harbored two or three coexisting 3'-ALK fusions, which might account for the different prognoses compared to patients harboring nonreciprocal/reciprocal ALK fusions. Furthermore, there were 6 patients harboring multiple ALK fusions coexisting with intergenic ALK fusions, which might also predict good response to ALK-TKIs therapy, because previous study found that intergenic-breakpoint rearrangement of ALK had favorable clinical outcomes and there may be a complicated splicing mechanism which could transcribe intergenic-breakpoint rearrangements into functional chimeric RNAs (33). However, the mechanism of the better response in patients with multiple ALK fusions is still unknown, and tumors with multiple ALK fusions are likely to be more reliant on the ALK signaling pathway, thus ALK-TKIs would be more effective in this condition (27). Thus, to clarify the mechanism of prolonged survival in those with multiple ALK fusions, preclinical studies to explain prolonged survival in patient with NSCLC harboring multiple ALK fusions and studies on the clinical outcome of a larger cohort of patients with multiple ALK fusions are warranted.

Furthermore, the prognosis in patients with brain metastases was unfavorable. Clinical trials with TKI treatment for patients with NSCLC and brain metastases have shown prolonged PFS, a high percentage of objective response, and improved quality of life (34). A previous study found that patients with NSCLC and brain metastases have a significantly higher rate of possessing several targetable genomic alterations, including ALK fusions (35). To further determine whether multiple ALK fusions could affect the prognosis of patients with brain metastases, we conducted an analysis of this patient group. We found that patients with brain metastases harboring multiple ALK fusions had favorable PFS, although there was no statistically significant difference in PFS between the single ALK fusion group and the multiple ALK fusions group, which was consistent with the clinical outcome in the patients overall. This likely demonstrates that any improvement in prognosis with multiple ALK fusions is overturned by the higher risk conferred by the presence of central nervous system (CNS) disease.

Limitations

This retrospective study is subject to several inherent limitations that warrant consideration. The primary concern is that a proportion of patients in the multiple ALK-fusion group were sourced through a literature search, a method that may not necessarily capture the full scope and detail of the patient characteristics, as compared to original case data obtained from clinical or hospital databases. Furthermore, the nature of the available data from these literature-sourced patients may be prone to publication or reporting bias, particularly as studies with negative results are less likely to be published. This potential bias could skew our findings and interpretations.

Additionally, a significant limitation is that some of the OS data of the patients included from the literature search were not mature at the time of our analysis. This lack of mature OS data creates a challenge when trying to accurately analyze survival outcomes. The absence of comprehensive and mature OS data precludes our ability to draw definitive conclusions about the long-term survival impact of multiple ALK-fusions in this population. This limitation is compounded by the potential for lead-time bias, given that survival measurements began from the time of diagnosis, which may vary widely among patients.

We acknowledge that these limitations may affect the robustness of our results and the strength of our conclusions. Therefore, the findings of this study should be interpreted cautiously and further validated in prospective studies with comprehensive and mature OS data.

Conclusions

Our study highlights the fact that multiple ALK fusions are not a rarity among patients with ALK-rearranged NSCLC. These findings challenge the conventional perception of the frequency of multiple ALK fusions and emphasize the importance of comprehensive genomic profiling to accurately capture the complex mutational landscape of NSCLC. This information underscores the necessity for more nuanced and detailed diagnostic testing that can recognize and differentiate between these multiple ALK fusions.

Most importantly, our results indicate a noteworthy association between multiple ALK fusions and improved PFS in NSCLC patients undergoing treatment with ALK-TKIs. This statistically significant correlation suggests a prognostic advantage for patients harboring multiple ALK fusions and reinforces the therapeutic value of ALK-TKIs in this molecularly defined subset of NSCLC.

Consequently, these insights pave the way for the potential use of multiple ALK fusions as predictive biomarkers for patients with NSCLC treated with ALK-TKIs. The identification of multiple ALK fusions may guide the selection of appropriate therapeutic strategies and help to predict patient response, potentially leading to improved patient outcomes.

Acknowledgments

Funding: This work was supported by the National Natural Science Foundation of China (Nos. 82072598, 81871890, and 91859203), the 1-3-5 Project for Disciplines of Excellence, West China Hospital, Sichuan University (No. ZYJC21052), the Science and Technology Program of Sichuan, China (No. 2020YFS0572), the Major Science and Technology Innovation Project of Chengdu City (No. 2020-YF08-00080-GX), the Central Guide Place-Free Exploration Project, Sichuan Provincial Department of Science and Technology (No. 2020ZYD005), and the Fundamental Research Funds for the Central Universities (No. SCU2022D025).

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://tlcr.amegroups.com/article/view/10.21037/tlcr-23-484/rc

Data Sharing Statement: Available at https://tlcr.amegroups.com/article/view/10.21037/tlcr-23-484/dss

Peer Review File: Available at https://tlcr.amegroups.com/article/view/10.21037/tlcr-23-484/prf

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tlcr.amegroups.com/article/view/10.21037/tlcr-23-484/coif). AD is an advisory board member in Sanofi, Amgen, and Foundation Medicine. The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013) and was approved by the Ethics Committee of West China Hospital of Sichuan University (No. 2022-1085). Individual consent for this retrospective analysis was waived.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

References

1. Thai AA, Solomon BJ, Sequist LV, et al. Lung cancer. Lancet 2021;398:535-54. [Crossref] [PubMed]
2. Soda M, Choi YL, Enomoto M, et al. Identification of the transforming EML4-ALK fusion gene in non-small-cell lung cancer. Nature 2007;448:561-6. [Crossref] [PubMed]
3. Sabir SR, Yeoh S, Jackson G, et al. EML4-ALK Variants: Biological and Molecular Properties, and the Implications for Patients. Cancers (Basel) 2017;9:118. [Crossref] [PubMed]
4. Tao H, Shi L, Zhou A, et al. Distribution of EML4-ALK fusion variants and clinical outcomes in patients with resected non-small cell lung cancer. Lung Cancer 2020;149:154-61. [Crossref] [PubMed]
5. He Y, Sun LY, Gong R, et al. The prevalence of EML4-ALK variants in patients with non-small-cell lung cancer: a systematic review and meta-analysis. Biomark Med 2019;13:1035-44. [Crossref] [PubMed]
6. Pagan C, Barua S, Hsiao SJ, et al. Targeting SLMAP-ALK-a novel gene fusion in lung adenocarcinoma. Cold Spring Harb Mol Case Stud 2019;5:a003939. [Crossref] [PubMed]
7. Du X, Shao Y, Gao H, et al. CMTR1-ALK: an ALK fusion in a patient with no response to ALK inhibitor crizotinib. Cancer Biol Ther 2018;19:962-6. [Crossref] [PubMed]
8. Ma L, Xiao J, Guan Y, et al. SDK1-ALK Fusion in a Lung Adenocarcinoma Patient With Excellent Response to ALK Inhibitor Treatment: A Case Report. Front Oncol 2022;12:860060. [Crossref] [PubMed]
9. Gu X, Wang W, Wu W, et al. Novel HIVEP1-ALK fusion in a patient with lung adenocarcinoma demonstrating sensitivity to alectinib: a case report. Transl Lung Cancer Res 2022;11:902-9. [Crossref] [PubMed]
10. Su C, Jiang Y, Jiang W, et al. STRN-ALK Fusion in Lung Adenocarcinoma with Excellent Response Upon Alectinib Treatment: A Case Report and Literature Review. Onco Targets Ther 2020;13:12515-9. [Crossref] [PubMed]
11. Xiang Y, Zhang S, Fang X, et al. Therapeutic Advances of Rare ALK Fusions in Non-Small Cell Lung Cancer. Curr Oncol 2022;29:7816-31. [Crossref] [PubMed]
12. Shaw AT, Solomon B, Kenudson MM. Crizotinib and testing for ALK. J Natl Compr Canc Netw 2011;9:1335-41. [Crossref] [PubMed]
13. Solomon BJ, Mok T, Kim DW, et al. First-line crizotinib versus chemotherapy in ALK-positive lung cancer. N Engl J Med 2014;371:2167-77. [Crossref] [PubMed]
14. Shaw AT, Kim DW, Nakagawa K, et al. Crizotinib versus chemotherapy in advanced ALK-positive lung cancer. N Engl J Med 2013;368:2385-94. [Crossref] [PubMed]
15. Tan DS, Araújo A, Zhang J, et al. Comparative Efficacy of Ceritinib and Crizotinib as Initial ALK-Targeted Therapies in Previously Treated Advanced NSCLC: An Adjusted Comparison with External Controls. J Thorac Oncol 2016;11:1550-7. [Crossref] [PubMed]
16. Peters S, Camidge DR, Shaw AT, et al. Alectinib versus Crizotinib in Untreated ALK-Positive Non-Small-Cell Lung Cancer. N Engl J Med 2017;377:829-38. [Crossref] [PubMed]
17. Hida T, Nokihara H, Kondo M, et al. Alectinib versus crizotinib in patients with ALK-positive non-small-cell lung cancer (J-ALEX): an open-label, randomised phase 3 trial. Lancet 2017;390:29-39. [Crossref] [PubMed]
18. Su Y, Long X, Song Y, et al. Distribution of ALK Fusion Variants and Correlation with Clinical Outcomes in Chinese Patients with Non-Small Cell Lung Cancer Treated with Crizotinib. Target Oncol 2019;14:159-68. [Crossref] [PubMed]
19. Li Y, Zhang T, Zhang J, et al. Response to crizotinib in advanced ALK-rearranged non-small cell lung cancers with different ALK-fusion variants. Lung Cancer 2018;118:128-33. [Crossref] [PubMed]
20. Yoshida T, Oya Y, Tanaka K, et al. Differential Crizotinib Response Duration Among ALK Fusion Variants in ALK-Positive Non-Small-Cell Lung Cancer. J Clin Oncol 2016;34:3383-9. [Crossref] [PubMed]
21. Lin JJ, Zhu VW, Yoda S, et al. Impact of EML4-ALK Variant on Resistance Mechanisms and Clinical Outcomes in ALK-Positive Lung Cancer. J Clin Oncol 2018;36:1199-206. [Crossref] [PubMed]
22. Wang S, Luo R, Shi Y, et al. The impact of the ALK fusion variant on clinical outcomes in EML4-ALK patients with NSCLC: a systematic review and meta-analysis. Future Oncol 2022;18:385-402. [Crossref] [PubMed]
23. Tao H, Liu Z, Mu J, et al. Concomitant novel ALK-SSH2, EML4-ALK and ARID2-ALK, EML4-ALK double-fusion variants and confer sensitivity to crizotinib in two lung adenocarcinoma patients, respectively. Diagn Pathol 2022;17:27. [Crossref] [PubMed]
24. Li Y, Duan P, Guan Y, et al. High efficacy of alectinib in a patient with advanced lung adenocarcinoma with 2 rare ALK fusion sites: a case report. Transl Lung Cancer Res 2022;11:100-10. [Crossref] [PubMed]
25. Wu X, Zhou H, He Z, et al. Coexistence of a novel CCNY-ALK and ATIC-ALK double-fusion in one patient with ALK-positive NSCLC and response to crizotinib: a case report. Transl Lung Cancer Res 2020;9:2494-9. [Crossref] [PubMed]
26. Zhang Y, Zeng L, Yang N, et al. P2. 14-51 dual ALK fusion partners as poor predictive marker in first line crizotinib treated ALK rearranged non-small cell lung cancer. J Thorac Oncol 2019;14:S849-50.
27. Kang J, Zhang XC, Chen HJ, et al. Complex ALK Fusions Are Associated With Better Prognosis in Advanced Non-Small Cell Lung Cancer. Front Oncol 2020;10:596937. [Crossref] [PubMed]
28. Cai C, Tang Y, Li Y, et al. Distribution and therapeutic outcomes of intergenic sequence-ALK fusion and coexisting ALK fusions in lung adenocarcinoma patients. Lung Cancer 2021;152:104-8. [Crossref] [PubMed]
29. Zhang Y, Zeng L, Zhou C, et al. Detection of Nonreciprocal/Reciprocal ALK Translocation as Poor Predictive Marker in Patients With First-Line Crizotinib-Treated ALK-Rearranged NSCLC. J Thorac Oncol 2020;15:1027-36. [Crossref] [PubMed]
30. Xia P, Zhang L, Li P, et al. Molecular characteristics and clinical outcomes of complex ALK rearrangements identified by next-generation sequencing in non-small cell lung cancers. J Transl Med 2021;19:308. [Crossref] [PubMed]
31. Li J, Zhang B, Zhang Y, et al. Concomitant mutation status of ALK-rearranged non-small cell lung cancers and its prognostic impact on patients treated with crizotinib. Transl Lung Cancer Res 2021;10:1525-35. [Crossref] [PubMed]
32. Rosenbaum JN, Bloom R, Forys JT, et al. Genomic heterogeneity of ALK fusion breakpoints in non-small-cell lung cancer. Mod Pathol 2018;31:791-808. [Crossref] [PubMed]
33. Yao Y, Yu Z, Ma Y, et al. Characterizing kinase intergenic-breakpoint rearrangements in a large-scale lung cancer population and real-world clinical outcomes. ESMO Open 2022;7:100405. [Crossref] [PubMed]
34. Rybarczyk-Kasiuchnicz A, Ramlau R, Stencel K. Treatment of Brain Metastases of Non-Small Cell Lung Carcinoma. Int J Mol Sci 2021;22:593. [Crossref] [PubMed]
35. Huang RSP, Harries L, Decker B, et al. Clinicopathologic and Genomic Landscape of Non-Small Cell Lung Cancer Brain Metastases. Oncologist 2022;27:839-48. [Crossref] [PubMed]