Background. The aim was to investigate the potential factors related with overall survival of oligometastatic non-small-cell lung cancer (NSCLC) patients. Methods. A literature search was conducted in databases including PubMed, Embase, and Cochrane library up to March 2017. The hazard radio (HR) as well as the corresponding 95% confidence interval (CI) were calculated, and all the statistics analysis was performed by the R 3.12. Heterogeneity was analyzed using I-squared and Cochran Q tests. Furthermore, sensitivity analysis was performed to evaluate the stability of results. Results. In total, 6 articles were included in the meta-analysis. Nodal status was significantly correlated with the overall survival rate of NSCLC oligometastatic patients (HR: 1.69, 95% CI: 1.23–2.32, Z=3.20, P=0.001). No significant relationship was found between overall survival rate of NSCLC oligometastatic patients and the indicators including sex, stage, smoker, age, and histology. Notably, sensitivity analysis on data evaluating relationship between patients survival and the stage and histology showed that results were reversed after removing one of the studies. Conclusions. Nodal status might be associated with the overall survival of oligometastatic NSCLC patients.
National Natural Science Foundation of China81472809815026538167298381703028Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)JX10231801Six Major Talent Peak Project of Jiangsu Province2013-WSN-0401. Background
Lung cancer is one of the leading causes of cancer-related deaths, and 80% among them are non-small-cell lung cancer (NSCLC) worldwide [1, 2]. Due to limited diagnostic technology, most NSCLC patients are diagnosed with advanced cancer [1, 3], and almost half among them have distant metastases (such as brain, adrenal glands, bone, or liver) [3, 4]. Although treatment technology develops continually, the survival of NSCLC patients is still poor due to the metastases [5, 6].
Oligometastasis is a notion that cancer patients develop 1–5 metastatic or recurrent lesions after treatment, which will affect the survival of patients [7]. Among them, patients with 1-2 metastases and recurrences show better prognosis than those with 3–5 metastases and recurrences [8]. Moreover, it has been reported that local therapy such as radiotherapy and surgery can effectively improve the survival of patients with postoperative oligometastases [9].
A recent meta-analysis put forward several prognostic factors associated with oligometastatic NSCLC treatment efficacy based on data of 757 individual patients [10]. The association between these factors (demographics and tumor status) and the survival of NSCLC patients with postoperative oligometastases has been investigated in previous studies. Several factors associated with overall survival evaluation have been reported as opposed to metachronous appearance of oligometastases [11–14]. However, the results of these studies are controversial. The study by Parikh et al. demonstrates that nodal involvement, pathology, and patient performance status may influence survival of oligometastatic NSCLC patients [15]. However, other studies do not support the above relationship [9, 16]. For example, the study by Griffioen et al. also does not find any association between the overall survival after oligometastatic NSCLC treatment and histology, age, smoke, and stage [17]. Therefore, it is not clear whether patient outcomes would have differed significantly if these oligometastatic NSCLC patients had various backgrounds.
Although these factors have been studied in several previous studies, the sample size and study content are limited in one clinical study. Therefore, in this study, we performed a meta-analysis pooling data of previously published clinical studies to systematically analyze the data and analyze the risk factors associated with the overall survival of NSCLC patients.
2. Materials and Methods2.1. Literature Search Strategy
Databases including PubMed (https://www.ncbi.nlm.nih.gov/pubmed), Embase (https://www.embase.com/), and Cochrane library (http://www.cochranelibrary.com/) were used for searching the English literature correlated with oligometastatic NSCLC. The search period was up to March 12, 2017. The keywords used for literature searching in Embase and Cochrane library mainly included (“Oligometastatic” or “oligometastasis”) AND (“NSCLC” or “nonsmall cell lung cancer”). The searching words in PubMed were as follows: (Oligometastatic[All Fields] OR oligometastasis[All Fields]) AND ((“carcinoma, nonsmall-cell lung”[MeSH Terms] OR (“carcinoma”[All Fields] AND “nonsmall-cell”[All Fields] AND “lung”[All Fields]) OR “nonsmall-cell lung carcinoma”[All Fields] OR “NSCLC”[All Fields]) OR “nonsmall cell lung cancer”[All Fields]).
2.2. Inclusion and Exclusion Criteria
The studies met all of the following criteria: (1) subjects were NSCLC patients with oligometastasis; (2) the risk factors of overall survival were investigated; and (3) the study was published in English.
The studies should be excluded if (1) the included data were not fully enough for statistical analysis; (2) the study was reviews, letters, or comments; (3) the newest study or the study with the most complete information was included when the data were repeatedly duplicated or the same population data were applied for multiple researches; and (4) the studies had obvious logic errors.
2.3. Data Extraction
The following data were recorded in a predesigned form: the name of the first author, study area, year of publication, study time, sample size, and the characteristics of objects (such as age and sex). The data extraction was performed independently by two investigators. Differences were resolved by discussion with the third investigators to ensure consistency of evaluation.
2.4. Statistical Analysis
The R 3.12 (R Foundation for Statistical Computing, Beijing, China, Package: Meta) was used to perform this meta-analysis [18]. The I-squared and Cochran Q tests were used to evaluate the heterogeneity among included studies [19]. It was defined that significant heterogeneity occurred when P<0.05 or I2>50%. If significant heterogeneity was observed among individual studies, the random effects model would be used to estimate the pooled effect of outcomes. If no obvious heterogeneity was observed, the fixed effect model would be used to pool the hazard radio (HR) as well as the corresponding 95% confidence interval (CI). The publication bias test was conducted using Egger’s test [20]. If there is a publication bias, the shear compensation method would be used to evaluate the previous numerical and analytical results. Sensitivity analysis was analyzed by ignoring a single document at a time and seeing if this document can reverse the overall combined effect [21]. For all these analyzes, P<0.05 indicated statistical significance.
3. Results3.1. Characteristics of Included Studies
The flowchart of article selection is shown in Figure 1. The initial literature search identified 248 articles from PubMed n=136, Embase n=91, and Cochrane library n=21. After excluding duplicates, 189 potentially relevant articles remained for further review. Then, 146 irrelevant studies were removed by scanning the titles or abstracts. Of the remaining 43 articles, 22 articles were excluded including 6 letter/editorial, 7 case series/reports, and 9 literature reviews. Then, 21 articles were full reviewed, 15 articles were excluded because the subjects in 8 articles were not only NSCLC, and outcomes in 7 articles were not shown. Finally, 6 studies [9, 15–17, 22, 23] were included and analyzed in this study.
Flow diagram of the study selection process.
The baseline characteristics of included studies are shown in Table 1. Briefly, a total of 6 studies including 565 oligometastatic NSCLC patients (female: n=232; male: n=333) were included in this meta-analysis. These patients received several different treatments strategy including surgical resection, whole brain radiation therapy, stereotactic radiosurgery, and chemoradiation. The publication year ranged from 2010 to 2016. The study time was between 1995 and 2015 (Table 1). The study region included China, Germany, United States, Japan, and Canada.
In this study, the risk factors of overall survival of oligometastatic NSCLC patients were analyzed, including sex (female vs. male), stage (stage I-II vs. stage III), nodal status (N0/N1 vs. N2/N3), smoker (smoker vs. nonsmoker), age (>60 vs. ≤60), and histology (others vs. adeno).
Significant heterogeneity among studies was found in the analyses for UICC-stage (I2=57.3%, P=0.07) and histology (I2=70.7%, P=0.03), so the data involved in the meta-analysis were pooled based on the random effects model. Moreover, no significant heterogeneity was observed on data evaluating the association between oligometastatic NSCLC occurrence and age (I2=0%, P=0.64), sex (I2=35.5%, P=0.21), N-stage (I2=25%, P=0.25), and smoker (I2=0%, P=0.89), and the fixed effects model was used.
The main results are shown in Table 2. We found that nodal status was significantly related to the overall survival rate of NSCLC oligometastatic patients (HR: 1.69, 95% CI: 1.23–2.32, Z=3.20, P=0.001). However, only two articles were included. As for the relationship between overall survival rate of NSCLC oligometastatic patients and the indicators including sex, stage, smoker, age, and histology, no significant effect on the survival rate of patients was found (Figure 2). Notably, sensitivity analysis on data evaluating relationship between patients survival and the stage and histology showed that results could be reversed after we removed one of the documents (Figure 3). Egger’s test did not detect publication bias in this meta-analysis P>0.05.
Fixed/random effects for oligometastatic non-small-cell lung cancer of overall survival.
Item
Group
Test of association
Model
Test of heterogeneity†,‡
Egger’s test for publication bias§
HR (95% CI)
Z
P
Q
P
I2 (%)
t
P value
Sex
Female vs. male
0.9373 [0.7194; 1.2211]
0.48
0.6312
Fixed
3.10
0.2122
35.5
0.4997
0.705
Stage
Stage I-II vs. stage III
0.6268 [0.3455; 1.1372]
−1.54
0.1243
Random
7.03
0.0709
57.3
0.7702
0.5217
Nodal status
N2/N3 vs. N0/N1
1.6853 [1.225; 2.3194]
3.20
0.0014
Fixed
1.33
0.2482
25.0
—
—
Smoker
Smoker vs. nonsmoker
1.1686 [0.8225; 1.6602]
0.87
0.3845
Fixed
0.02
0.8953
0
—
—
Age
>60 vs. 60
0.9812 [0.7474; 1.2881]
−0.14
0.8913
Fixed
0.87
0.6479
0
0.70602
0.6086
Histology
Others vs. adeno
0.6056 [0.2762; 1.3277]
−1.25
0.2105
Random
6.82
0.0330
70.7
4.7318
0.1326
†Random effects model was used when the P value for heterogeneity test is <0.05; otherwise, the fixed effect model was used. ‡P<0.05 is considered statistically significant for Q statistics. §Egger’s test to evaluate publication bias, P<0.05, is considered statistically significant. OR: odds ratio. CI: confidence interval.
Meta-analysis for the association of survival of oligometastatic non-small-cell lung cancer patients with sex (a), stage (b), nodal status (c), smoke (d), age (e), and histology (f).
Sensitivity analysis for the association of survival of oligometastatic non-small-cell lung cancer patients with sex (a), stage (b), nodal status (c), smoke (d), age (e), and histology (f).
4. Discussion
Although advanced NSCLC is associated with low survival, oligometastatic NSCLC patients have a better prognosis [13]. In order to evaluate the overall survival for these patients more precisely, we performed the meta-analysis to evaluate the potential factors associated with the survival of oligometastatic NSCLC patients. We found that nodal status was significantly related with the overall survival rate of NSCLC oligometastatic patients. However, no significant relationship was found between sex, stage, smoker, age, and histology and the overall survival of oligometastatic NSCLC patients. However, some factors may affect the association of overall survival with sex, stage, smoker, age, and histology.
Cancer patients with 1–5 metastatic or recurrent lesions after treatment are considered to have oligometastases. The role of metastatic status in the overall survival of oligometastatic NSCLC is similar to that reported in a previous analysis that the metastases status, such as number and location of metastases, was associated with the survival of patients with NSCLC. Similarly, a meta-analysis also demonstrated that N1-stage or N2-stage (vs. N0) was a predictive factor for a decreased OS based on 757 patients [10]. For patients with synchronous oligometastases, Mordant et al. demonstrated that the absence of nodal mediastinal involvement was associated with improved overall survival [24]. In the present study, we also showed that nodal status was a positive prognostic factor. Thus, in order to pursue definitive treatment for these patients, it should be recommended that factors such as nodal involvement should be fully considered.
There were obvious histology differences between adenocarcinoma and nonadenocarcinoma NSCLC. These histology differences may result in different responses to the same treatment. Moreover, it is also reported that the histology can be used for predicting the survival of NSCLC patients with brain metastases [25, 26]. Notably, only two included studies reported association between N-stage and survival of oligometastatic NSCLC patients, and the results in these two studies were inconsistent [15, 16]. As for the evaluation of UICC-stage and overall survival of oligometastatic NSCLC patients, significant heterogeneity was found among studies. Furthermore, significant evidences were also found among the studies evaluating association between histology and overall survival of oligometastatic NSCLC patients [14]. In addition, no association of overall survival with age, sex, and smoke was found in oligometastatic NSCLC patients. However, a previous study showed that male sex, age ≥80 years, and smoking were associated with the shorter survival time in NSCLC patients aged ≥70 years [27]. Moreover, the association of sex, age, and smoke with metastases in NSCLC patients has been reported. The discrepancy between the findings in those studies and those in ours may be explained by confounding factors such as sex ratio, county distribution, and included sample size. Although we found that no significant relationship was found between sex, stage, smoker, age, and histology and the overall survival of oligometastatic NSCLC patients, further studies should be performed to explore these influence factors.
There were some limitations in this meta-analysis. Firstly, significant heterogeneities occurred when we pooled data from individual studies evaluating the role of histology and stage in overall survival of oligometastatic NSCLC patients. For the meta-analysis, heterogeneity degree is an important indicator of meta-analysis validity [28]. According to the limited enrolled sample size, subgroup analysis could not be performed. It could not be repudiated that patients baseline characteristics, site of oligometastatic disease (e.g., brain, bone, and adrenal glands), and treatment strategy might be blamed for the sources of the obvious heterogeneities. Second, many factors, such as tumor size and metastasis, could not be analyzed in this meta-analysis due to lack of available data. The risk factors for progression-free survival should be determined in further studies. Thus, it should be recommended that further study with larger sample size and homogeneity of data would be designed to verify the current conclusion.
5. Conclusion
In conclusion, our study suggested that nodal status might be a prognostic factor for oligometastatic NSCLC patients. However, the number of included studies was small, and further attention should be paid to this research.
AbbreviationsNSCLC:
Non-small-cell lung cancer
HR:
Hazard radio
CI:
Confidence interval.
Data Availability
The data used to support the findings of this study are available from the corresponding author upon request.
Conflicts of Interest
The authors declare that they have no potential conflicts of interest.
Authors’ Contributions
YS, JX-Y, and NHY contributed to the study design, conducting the study, analyzing the data, and writing of the manuscript. MS and WX-D contributed to the data collection and conducting the study. WR-J and XC-S contributed to data interpretation and discussion. All the authors read and approved the final manuscript.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (nos. 81472809, 81502653, 81672983, and 81703028), the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD) (no. JX10231801), and the Six Major Talent Peak Project of Jiangsu Province (no. 2013-WSN-040).
KomakiR.TsaoA. S.MehranR. J.Non-small cell lung cancer2012New York, NY, USASpringer4562TorreL. A.BrayF.SiegelR. L.FerlayJ.Lortet-TieulentJ.JemalA.Global cancer statistic, 201220156528710810.3322/caac.212622-s2.0-84924271853D’AddarioG.FrühM.ReckM.Metastatic non-small-cell lung cancer: ESMO clinical practice guidelines for diagnosis, treatment and follow-up2016215v116v11910.1093/annonc/mdq1892-s2.0-77954321859SørensenJ. B.HansenH. H.HansenM.DombernowskyP.Brain metastases in adenocarcinoma of the lung: frequency, risk groups, and prognosis1988691474148010.1200/JCO.1988.6.9.14742-s2.0-0024271627JohungK. L.YehN.DesaiN. B.Extended survival and prognostic factors for patients with ALK-rearranged non-small-cell lung cancer and brain metastasis201634212312910.1200/jco.2015.62.01382-s2.0-84954318418ZhouQ.YangJ.ZhangX.Overall survival in patients with advanced non-small cell lung cancer harboring concomitant EGFR mutations and ALK rearrangements: A cohort study20143215e1901010.1200/jco.2014.32.15_suppl.e19010GhalyG.HarrisonS.KamelM. K.Predictors of survival after treatment of oligometastases after esophagectomy2018105235736210.1016/j.athoracsur.2017.10.0392-s2.0-85038877749SalamaJ. K.ChmuraS. J.MehtaN.An initial report of a radiation dose-escalation trial in patients with one to five sites of metastatic disease200814165255525910.1158/1078-0432.ccr-08-03582-s2.0-52649088246YanoT.HaroA.YoshidaT.Prognostic impact of local treatment against postoperative oligometastases in non-small cell lung cancer2010102785285510.1002/jso.217502-s2.0-78649671323AshworthA. B.SenanS.PalmaD. A.An individual patient data metaanalysis of outcomes and prognostic factors after treatment of oligometastatic non-small-cell lung cancer201415534635510.1016/j.cllc.2014.04.0032-s2.0-84908249715De RuysscherD.Radical treatment of synchronous oligometastases from NSCLC201617121625162610.1016/s1470-2045(16)30533-22-s2.0-85002779879De WolfJ.BellierJ.Lepimpec-BarthesF.Exhaustive preoperative staging increases survival in resected adrenal oligometastatic non-small-cell lung cancer: a multicentre study201752469870310.1093/ejcts/ezx1932-s2.0-85030662729OnestiC. E.IaconoD.AngeliniS.Unexpected long survival of brain oligometastatic non-small cell lung cancer (NSCLC) treated with multimodal treatment: a single-center experience and review of the literature20165671271910.21037/tlcr.2016.09.012-s2.0-85010210748SuS.HuY. X.OuyangW. W.Might radiation therapy in addition to chemotherapy improve overall survival of patients with non-oligometastatic stage IV non-small cell lung cancer?: secondary analysis of two prospective studies201616190810.1186/s12885-016-2952-32-s2.0-84997824402ParikhR. B.CroninA. M.KozonoD. E.Definitive primary therapy in patients presenting with oligometastatic non-small cell lung cancer201489488088710.1016/j.ijrobp.2014.04.0072-s2.0-84903268819FleckensteinJ.PetroffA.SchäfersH.-J.WehlerT.SchöpeJ.RübeC.Long-term outcomes in radically treated synchronous vs. metachronous oligometastatic non-small-cell lung cancer20161634810.1186/s12885-016-2379-x2-s2.0-84971500784GriffioenG. H. M. J.ToguriD.DaheleM.Radical treatment of synchronous oligometastatic non-small cell lung carcinoma (NSCLC): patient outcomes and prognostic factors20138219510210.1016/j.lungcan.2013.07.0232-s2.0-84884418406BilalJ.BerlinbergA.BhattacharjeeS.TrostJ.RiazI. B.KurtzmanD. J. B.A systematic review and meta-analysis of the efficacy and safety of the interleukin (IL)-12/23 and IL-17 inhibitors ustekinumab, secukinumab, Ixekizumab, brodalumab, guselkumab, and tildrakizumab for the treatment of moderate to severe plaque psoriasis201829613710.1080/09546634.2017.14225912-s2.0-85044475552FreemanM. F.TukeyJ. W.Transformations related to the angular and the square root195021460761110.1214/aoms/1177729756BowdenJ.Davey SmithG.BurgessS.Mendelian randomization with invalid instruments: effect estimation and bias detection through Egger regression201544251252510.1093/ije/dyv0802-s2.0-84936755918ZhaoY.LiZ.ZhangL.The TNF-alpha-308G/A polymorphism is associated with type 2 diabetes mellitus: an updated meta-analysis2014411738310.1007/s11033-013-2839-12-s2.0-84891938555BaiH.XuJ.YangH.Survival prognostic factors for patients with synchronous brain oligometastatic non-small-cell lung carcinoma receiving local therapy201694207421310.2147/OTT.S1066962-s2.0-84978473799CollaudS.StahelR.InciI.Survival of patients treated surgically for synchronous single-organ metastatic NSCLC and advanced pathologic TN stage201278323423810.1016/j.lungcan.2012.09.0112-s2.0-84868300148MordantP.ArameA.De DominicisF.Which metastasis management allows long-term survival of synchronous solitary M1b non-small cell lung cancer?201241361762210.1093/ejcts/ezr0422-s2.0-84861431610GuoS.ReddyC. A.ChaoS. T.Impact of non-small cell lung cancer histology on survival predicted from the graded prognostic assessment for patients with brain metastases201277238939310.1016/j.lungcan.2012.03.0282-s2.0-84863774618PutoraP. M.EssS.PanjeC.Prognostic significance of histology after resection of brain metastases and whole brain radiotherapy in non-small cell lung cancer (NSCLC)201532214314910.1007/s10585-015-9699-02-s2.0-84925466946HsuC.-L.ChenJ.-H.ChenK.-Y.Advanced non-small cell lung cancer in the elderly: the impact of age and comorbidities on treatment modalities and patient prognosis201561384510.1016/j.jgo.2014.09.1782-s2.0-84920872437MorenoS. G.SuttonA. J.ThompsonJ. R.AdesA. E.AbramsK. R.CooperN. J.A generalized weighting regression-derived meta-analysis estimator robust to small-study effects and heterogeneity201231141407141710.1002/sim.44882-s2.0-84863414972