The effectiveness of targeted therapy for recurrence or metastasis adenoid cystic carcinoma: a systematic review and meta-analysis

Abstract Background and purpose Several clinical studies have demonstrated the potential of molecular-targeted agents for the treatment of recurrent or metastatic adenoid cystic carcinoma (R/M ACC). However, there is currently no consensus regarding the efficacy of molecular-targeted agents for patients with R/M ACC. This study aimed to evaluate the therapeutic efficacy and safety of molecular-targeted agents in patients with R/M ACC and provide insights to guide clinical decision-making. Materials and methods Five databases (PubMed, Embase, Cochrane, ProQuest, and Scopus) were searched based on the search strategy and selection criteria. Primary endpoints were objective response rate (ORR) and progression-free survival (PFS). The secondary endpoints were disease control rate (DCR), overall survival (OS), metastatic sites, and adverse events (AE). Pooled estimates were calculated using a random-effects meta-analysis. Results Finally, 28 studies, involving 849 patients, were included. The most common metastatic sites were the lungs, bones, liver, lymph nodes, and kidneys. The pooled ORR was 4.0% (95% CI, 0.7–8.8%), the pooled DCR was 80.5% (95% CI, 72.2%–87.7%). Compared with other-target drugs, multiple kinase inhibitors (MKIs) improved the ORR (pooled ORR for single-target drugs vs. MKIs: 5.9% vs. 0%). The combination of MKIs and immune checkpoint inhibitors (ICIs) had a significantly higher ORR (17.9% in the axitinib + avelumab group). The pooled median PFS and OS were 8.35 and 25.62 months, respectively. MKIs improved the median PFS compared to other-target drugs (9.43 months vs 5.06 months). In addition, the most common adverse events (AEs) were fatigue (51.6%), hypertension (44.2%), and nausea (40.0%), followed by hand-foot skin syndrome (36.8%), diarrhoea (34.4%), weight loss (34.2%), anorexia (31.8%), rash (31.7%), and headache (29.0%). Conclusion The findings of this study suggest that MKIs have a better therapeutic efficacy than single-target drugs in patients with R/M ACC. Future studies are warranted to verify the synergistic role of the combination strategy of MKIs plus ICIs, given the limited number of studies on this topic conducted and published to date.


Introduction
adenoid cystic carcinoma (acc) mostly develops in the salivary glands [1] and accounting for 10-20% of salivary gland tumours [2].however, nearly 50-60% of these patients will experience a recurrence of disease, and common metastatic sites are the lungs, bones, and liver [3,4].
histologically, acc is categorized by its predominant morphological patterns, including cribriform, tubular, or solid types, which plays a pivotal role in determining the tumour grade [5].Recent evidences suggested two prognostic acc molecular subtypes: acc-i (37%) and acc-ii (63%).acc-i is featured with overexpression of MYc, and mRNa splicing.additionally, acc-i is enriched in NOtch-activating mutations, leading to a significantly worse prognosis.On the other hand, acc-ii is demonstrated with upregulation of tP63 and receptor tyrosine kinases (aXl, Met, eGFR), showing a less aggressive clinical course [6].
surgical resection is a top priority for operable acc patients.Otherwise, inoperable local advanced patients are recommended to receive radiotherapy.For recurrence/metastatic (R/M) acc, these patients are treated with systemic therapy, expectant management, selected metastasectomy or best supportive care.[7] the systemic therapy for R/M acc mainly includes chemotherapy and targeted therapy, but the therapeutic regime remains controversial at present because of the lack of high-quality evidence-based clinical practice.the early studies had shown that the objective response rate of single-agent chemotherapy treating acc, such as cisplatin [8] and gemcitabine [9], are less than 12%.Notably, the objective response rates for cyclophosphamide-doxorubicin-cisplatin (caP) [10][11][12][13] and cisplatin-vinorelbine [14,15] range from 18% to 31% but with high incidence of side effects [16]. in the past decade, several clinical trials had explored the potentiality of various targeted drugs in R/M acc patients.which gradually become the most promising therapeutic regime, including multiple kinase inhibitors (MKis), NOtch-targeted therapies, chromatin remodelling agents, agents targeting the Pi3K signalling (the phosphatidylinositol-3-kinase (Pi3K)/aKt/ mammalian target of rapamycin (mtOR) axis), MYB inhibitors, eGFR inhibitors, agents targeting the mouse double minute 2 homolog (MDM2)-p53 axis, and prostate-specific membrane antigen (PsMa)-targeting therapy [17,18].however, the curative effect of molecular targeted agents (ranging from 0-15.6%) varies widely among different trials.For example, the ORR and DcR of apatinib (also known as rivoceranib) was 46.2%, 98.5% respectively in Guopei Zhu et al. ' report [19], while only 15.3% and 90.3% in another clinical trial [20], as such, in the tKi treatment of acc, there is currently no clearly defined optimal choice.similarly, in various targeted therapies, there is no well-designed trial for head-to-head evaluation of the efficacy and safety of different targeted drugs.therefore, we sought to performed a meta-analysis to investigate the therapeutic benefit of targeted drugs in R/M acc patients, aiming to provide a reference for clinical practice.

Materials and methods
We conducted a systematic literature review and meta-analysis following the Preferred Reporting items for systematic Reviews and Meta-analyses (PRisMa) reporting guidelines [21].this protocol is available online at PROsPeRO (cRD42022376157).PROsPeRO Registration Number: cRD42022376157; https://www.crd.york.ac.uk/prospero/display_record.php?iD= cRD42022376157

Search strategy
two investigators independently searched five databases: PubMed, embase, cochrane, ProQuest, and scopus.the search was performed until November 30, 2022, and the detailed search strategy is provided in the supplemental Data. the search strategy utilized Medical subject heading (Mesh) terms and all synonyms for carcinoma, adenoid cystic in combination with Mesh, and all synonyms for molecular-targeted therapy.to ensure maximum sensitivity and to identify all relevant studies, conference abstracts were also considered.a PRisMa flow diagram is shown in Figure 1.

Study election and data extraction
the inclusion criteria for this study were as follows: (1) patients diagnosed with locally recurrent and/or metastatic adenoid cystic carcinoma.(2) Patients receiving targeted drug therapy as part of their treatment.these patients may also have received other treatments, such as radiotherapy or chemotherapy.(3) sufficient data available for quantitative meta-analysis, including the reporting of a comparative OR hazard radio for at least one outcome measure such as progression-free survival (PFs), overall survival (Os), disease control rate (DcR), or grade ≥ 3 treatment-related adverse events, were used to select eligible studies for inclusion in the meta-analysis.
the exclusion criteria were as follows: (1) reviews, surveys, letters, case reports, book chapters, and commentary articles; (2) patients who did not receive targeted drug therapy, the content of the study deviated from the aims of this study; (3) studies involving nonhuman subjects; (4) written in a language other than english; (5) literature that did not have original text; (6) literature that did not contain data; (7) studies with fewer than 10 patients; and (8) studies with less than 6 months of follow-up.

Study election
after conducting the literature search, two investigators eliminated all duplicate studies obtained from different databases.We then independently screened the titles and abstracts of all the remaining articles to exclude studies that did not meet the inclusion criteria.the researchers carefully read the complete literature for possible inclusion and screened those that ultimately met the criteria.any disagreements regarding study eligibility that remain after discussion can be resolved by consulting another investigator.
By eliminating duplicates and screening for relevance based on the inclusion criteria, investigators can reduce the risk of bias and ensure that their review is based on high-quality studies.

Data extraction
the following information was extracted from each included study: first author, year of publication, country, age, mean age, study type, invention drags, total number of patients, number of males and females, number of all adverse events, median age, follow-up time, primary end-point, secondary end-point, criteria for response, and criteria for adverse events aes. the clinical responses included progression-free survival (PFs), overall survival (Os), disease control rate (DcR), objective response rate (ORR), complete response (cR), stable disease (sD), partial response (PR), and progressive disease (PD).
Os was defined as the time between the date of treatment initiation and death for any cause, whereas PFs was defined as the time between treatment initiation and first assessment of progression or death for any cause.cR, complete remission; PR, partial remission; sD, stable disease; and PD, progressive disease; aes, adverse events.the ORR refers to the objective response rate, which is the sum of the proportions of complete and partial remission.DcR refers to the disease control rate, which is the percentage of cases with remission (PR + cR) and stable disease (sD) after treatment among evaluable cases.

Assessment of study quality
two investigators assessed the risk of bias based on the original study using the Newcastle-Ottawa scale (NOs) for cohort or case-control studies.the included single-arm studies were assessed using the methodological index for non-randomized studies (MiNORs) [22].the JBi critical appraisal checklist for case series assesses retrospective studies without a comparison group [23].

Statistical analysis
a random-effects model was used to pool the single-group rates of DcR and ORR.Given the differences in each study intervention, we conducted a meta-analysis by classifying the included studies into RtK and other treatment subgroups.We used stata software (version 14.0) for data analyses.then, we analyzed their heterogeneity and sensitivity, and we show pictures of the funnel plot and sensitivity analysis in the supplemental Figure .as most studies did not report detail data about PFs and Os, the survival data was extracted from Kaplan-Meier (K-M) curves using software engauge Digitizer version 11.3, then survival curve is pooled by 'Metasurv' packages in Rstudio (R version 4.3.0)[24,25].

Systematic review and study characteristics
the literature search yield 1607 publications, from 50 eligible articles, 28 studies were included according to the inclusion criteria [19,20,.Most of the studies were single-arm Phase ii trials conducted in 849 patients with R/M acc. the study's characteristics are listed in table 1. the effectiveness of multiple kinase inhibitors (MKis) was reported in 19 studies, eGFR-tKis in four studies, targeting the Pi3K/aKt/mtOR axis (aKt inhibitor and everolimus) in two studies, chromatin remodelling agents (vorinostat) in one study, mtOR inhibitor (everolimus) in one study, and NOtch inhibitor (al101) in one study, MYB inhibitor (atRa) in one study (table 2). the median age ranged from 46 (17-67) years to 63 (31-73) years, while the median follow-up time ranged from 4 to 77 months.the most common metastatic sites were the lungs, bones, liver, lymph nodes, and kidneys.Detailed information is provided in supplemental table s1.

Quality assessment
the quality of the eight studies was assessed using the Newcastle-Ottawa Quality assessment Form for cohort studies (NOs), with scores ranging from 6 to 8. twenty single-arm studies were assessed using the MiNORs index score ranging from 13 to 15 points, which was acceptable for the present meta-analysis.One retrospective study without comparison was included after it was assessed using the JBi critical appraisal checklist for case series.the details of the quality assessments are shown in table 3.

Evaluation of efficacy outcomes
Of the 28 studies, three studies used multiple drugs and 25 used single drugs.We divided the single-drug group into six groups, three of which had only one study, which we tabulated separately to analyze ORR and DcR, and the other three were divided into MKi, eGFR inhibitor, and targeting the Pi3K/aKt/mtOR axis, and analyzed the DcR and ORR separately for these three groups.We also analyzed DcR and ORR separately for the other three multi-drug studies.
as shown in Figure 2, the pooled ORR was 4.0% (95% ci, 0.7%-8.8%). in the subgroup analysis, the pooled ORR was higher in the group of MKis (5.9%, 95% ci, 1.5%-12.3%)than in the other two groups of single-target drugs (0%, 95% ci, 0-3.5%).the forest plot indicated that MKis of apatinib (46.2% ORR) and NOtch inhibitors (15.4% ORR) were potential candidates, but the first-generation eGFR inhibitors, including Gefitinib and lapatinib, might not be efficient when treating patients with R/M acc. the combination of eGFR and chemotherapy also had a potential synergistic effect, with an ORR of 42.9% for cetuximab combined with chemotherapy (supplement table s2) [32]. in addition, the combination of immune checkpoint inhibitors (icis) and MKis had a potential synergistic effect; for instance, axitinib combined with avelumab reached a 17.9% ORR (supplement table s2).

Sensitivity analysis and publication bias
We conducted a sensitivity analysis of 28 articles and obtained the following results: p = 0.11 (95%ci) (0.04, 0.18).this indicates that none of the articles would affect the meta-analysis results, which means that our study was very stable (supplementary Figures s1  and s2).
egger's and Begg's tests were performed to evaluate publication bias.Funnel plot the pooled DcR in R/M acc.P value for egger: 0.137, P value for Begg:0.257(supplementary Figure s3).the test results of the pooled ORR did not show significant publication bias among the included studies (p = 0.02 for egger's test and p = 0.593 for Begg's test) (supplementary Figure s4).

Discussion
adenoid cystic carcinoma is considered as a slow growing tumour with relatively high 5-year survival rate (90.3%).Nonetheless, nearly 60% patients suffer a recurrence after initial treatment.the optimized treatment of R/M acc is remained to be explored.this systematic review and meta-analysis showed that the pooled ORR of R/M acc patients receiving any targeted therapy was 4%. the subgroup analysis indicated that MKis was better for patients with R/M acc when comparing with other-target drugs (ORR, 5.9% vs 0%).
this meta-analysis found that MKis, especially apatinib in the largest cohort study [19], were significantly better in terms of ORR and median PFs than other-target drugs in patients with R/M acc.however, another clinical trial involving apatinib (now rivoceranib) has reported a modest ORR (15.3%) [20].the objective response rate (ORR) for recurrent/metastatic acc after treatment with MKi mostly ranged from 0% to 15.6%.however, the addition of MKis barely improved the DcR compared with other-target drugs.hence, there is currently no tyrosine kinase inhibitor (tKi) that distinctly stands out as the preferred choice for acc.
MKis (except imatinib) block VeGF-VeGFR signalling and inhibit VeGF-mediated endothelial cell migration and proliferation.Reports have shown that VeGF is overexpressed in acc compared to benign salivary gland tumours with low VeGF expression levels [52,53].this partially explains the higher ORR of MKis to single-target drugs and indicates the importance of targeting VeGF-VeGFR signalling.imatinib targets BcR-aBl, PGFRa, and c-Kit and has revolutionized the management of chronic myeloid leukaemia and gastrointestinal stromal tumours, but failed to improve ORR and DcR in patients with R/M acc [54,55]. in the study conducted by Kang et al. in 2021 [47], there is a lower response rate of axitinib, but 3 patients crossed over to the experimental group, resulting in a response rate of 11.5%, Median PFs in the axitinib arm was 10.8 months.as compared to the previous study with a single-arm design, Kang et al. 's study had a sufficient sample size and excluded patients prior exposure to anti-angiogenic drugs.therefore, Kang et al. 's study is more convincing.Furthermore, the treatment with single agent targeting the cKit, eGFR Fibroblast Growth Factor Receptor (FGFR), and Protein Kinase B (aKt) pathways did not significantly improve clinical outcome of patients with R/M acc [56].More efforts are required to identify the therapeutic target for acc.eGFR is commonly overexpressed in acc, making it a potential therapeutic target [57].in this study, no response was observed in phase ii trials testing the first-generation eGFR inhibitors Gefitinib and lapatinib.One possible reason is that eGFR gene mutations only account for approximately 10% of acc patients, although the expression of the eGFR protein is common [58,59].Moreover, targeting eGFR led to the accumulation of stem-like cells in acc, which contributed to tumour development [60].Based on these studies, eGFR inhibitors may not be appropriate for patients with R/M acc.
Recent studies found that acc tumours could be categorized into two main subtypes, in which acc-i exhibited MYc overexpression and NOtch mutation with poor prognosis, and acc-ii exhibited P63 overexpression and RtK upregulation with improved prognosis [6,61].consistent with Ferrarotto et al. 's report (2022) [6], the gene expression analysis of acc revealed identified potential therapeutic targets including G2-M checkpoint genes, e2F, MYc targets, iFN, MtORc1, Ras signalling and the FGF/iGF/Pi3K and NOtch pathways [62].Beyond the good prognosis for primary acc patients, the newly recognized subtype with enrichment of NOtch1 activating mutations results in a short median Os of 3.4 years [6,17].thus, targeting NOtch signalling may improve the outcome of patients with acc-i.al101 is a γ-secretase inhibitor that inhibited acc xenograft growth in a preclinical study.early results from a phase 2 trial investigating al101 (Nct03691207) showed promising ORR in patients with R/M acc.Overall, the molecular classification of R/M acc should be further investigated in the future to guide the cinical decisions regarding specific targeted agents.combination therapy with targeted therapy and chemotherapy or immunotherapy is promising.Preliminary studies, such as those by savarese et al. [63], showed that combining drugs like vorinostat or olaparib with standard chemotherapy agents like cisplatin and doxorubicin was more effective than monotherapy.Ongoing clinical trials are exploring the efficacy of such combinations in improving patient survival rates and treatment effects, particularly in R/M acc, with early results indicating synergistic effects and good tolerability [32].currently, due to the small sample size in clinical studies, it is challenging to identify subgroups that benefit from them, highlighting the need for effective predictive biomarkers.Further research is needed to understand the biological basis of immune checkpoint inhibitor resistance and to develop more effective treatment strategies, especially considering the diversity of MKis.
similar to other reports about adverse events of targeted therapy, skin changes, including rash (29.4%) and hand-foot syndrome (36.8%), were common according to the pooled data. in addition, we found a high pooled incidence of hypertension (44.2%), partially due to treatment with VeFGR inhibitors, such as lenvatinib, apatinib, axitinib, regorafinib, and anlotilib.Other common adverse events, including nausea, anorexia, headache, anaemia, and thrombocytopenia, were comparable to the incidence of targeted therapy in other cancers.specifically, fatigue (52.5%), hypertension (46.1%), and nausea (43.4%) are the most common adverse events of patients receiving MKis, while diarrhoea was associated with NOtch inhibitors. in brief, there were no additional adverse events in patients with R/M acc receiving targeted therapy when compared to other cancers [64,65].
although only approximately 10% of patients with acc have distant metastasis at diagnosis, more than half of the patients experience distant metastasis when they have recurrence.according to an early study, the lung was the most common site of metastasis, with an incidence of approximately 90%, followed by the bone and brain.the pooled data from the 16 studies that reported metastasis sites were consistent with earlier findings.the pooled incidences of lung and bone metastases were 81.6% and 25.8%, respectively.in contrast to other reports, the incidence of brain metastasis was 4.8%.Moreover, the liver and kidney should also be assessed carefully, with incidences of 23.7% and 9.7%, respectively.
this study had several limitations.First, the heterogeneity was high in the pooled and subgroup analyses.since all studies included were non-randomized

Figure 1 .
Figure 1.flow diagram of included and excluded studies.

Figure 2 .
Figure 2. Pooled results of oRR represented by forest plots.The large diamond at the bottle of the plot represents the pooled rate of all studies.The width of the diamond represents with 95% ci.

Figure 3 .
Figure 3. Pooled results of dcR by forest plots.The large diamond at the bottle of the plot represents the pooled rate of all studies.The width of the diamond represents with 95% ci.

Figure 4 .
Figure 4. Pooled Kaplan-Meier survival curves of Acc treated with targeted therapy.(A) Pooled Kaplan-Meier Pfs curves of Acc targeted therapy; (B) Pooled Kaplan-Meier os curves of Acc targeted therapy; (c) Pooled summary progression-free survival curves of Acc treated with single-target targeted therapies; (d) Pooled summary progression-free survival curves of Acc treated with MKi targeted therapies.Blue lines represent survival curves for individual studies.solid red lines represent summary survival curves with 95% cis (dashed red lines).
n: number; M/f: Male/female; l:locally advanced disease; M:metastases; cR: complete response; PR: partial response; sd: stable disease; Pfs: progression-free survival; os: overall survival; Ae: adverse events; oRR: objective response rate, sum of cR and PR; dcR: disease control rate,sum of cR, PR and sd; doR: duration of response; TTP: time to progress; BoR: best overall response; cBR: clinical benefit rate; TGR: tumour growth rate; Qol: quality of life; RecisT: response evaluation criteria of solid tumour; cTcAe: common terminology criteria for adverse events; sYsUcc: sun yat-sen university cancer center; nA: not available.were

Table 2 .
Response rate to targeted therapies of included clinical trials.

Table 3 .
Quality assessment of included studies.

Table 4 .
incidence rates of the most common adverse events across all grades and grade 3 or higher.VeGFR inhibitors) and NOtch inhibitors, may improve outcomes.the combination strategy of molecular-targeted therapy with widely studied immunotherapy should be investigated in the future.Moreover, understanding the molecular classification of R/M acc is important for building personalized molecular targeted treatments, and more research is needed to achieve this goal.this study was supported by grants from the National Natural science Foundation of china (No. 81972857 to Y Wang; No. 82073347 to YZ Wu; No. 82373196 to JD sui),

Table 5 .
The summary of adverse events of included studies.Multiple Kinase inhibitors; eGfR: epidermal growth factor receptor; Pi3K: phosphatidylinositol-3-kinase; nA: not available.chongqing science and health Joint Medical Research Project (No. 2022ZDXM028 to JD sui; No. 2023GGXM002 to YZ Wu), the Natural science Foundation of chongqing city (No. cstc2021jxjl130034 to YZ Wu; No. cstB2023 NscQ-MsX0709 to JD sui). the chongqing talent Program (no.cstc2021ycjh-bgzxm0023 to Y Wang).