3.1 Article retrieval and selection
The process of literature searching and study inclusion was shown in Figure 1. In total, 2324 articles were retrieved in databases, after delete repeated and widely different articles, 248 articles were retrieved. After reading the titles of the abstract, only 42 remained. After reading the articles and excluding articles that did not meet the inclusion criteria, 16 articles were finally selected. In addition, after reading the references of relevant review articles, 4 articles on related clinical controlled research were selected. Thus, 20 articles were selected in total involving 5643 patients.
3.2 General characteristics and quality evaluation of the articles
The general characteristics of all articles are shown in Table 1[17–29]. Quality evaluation of the articles was conducted by two researchers independently as it is subjective in nature. A third researcher evaluated the disputed results and resolved the disputes.
Table 1
General characteristics of the selected articles
Author
|
Year
|
Research type
|
Country
|
D2
|
D2+
|
D2
|
D3
|
D2(year)
|
D2+(year)
|
|
|
|
|
cases
|
cases
|
male/female
|
male/female
|
age
|
age
|
Maeta[17]
|
1999
|
RCT
|
Japan
|
35
|
35
|
21/14
|
20/15
|
60±11
|
59±9
|
Ikeguchi [40]
|
2000
|
Non-RCT
|
Japan
|
524
|
221
|
NA
|
NA
|
NA
|
NA
|
Jiang[18]
|
2000
|
RCT
|
China
|
32
|
21
|
19/13
|
11/10
|
46-83
|
34-84
|
Yan-Chang[19]
|
2002
|
Non-RCT
|
China
|
50
|
36
|
NA
|
22/14
|
29-70
|
34-68
|
Bostanci[20]
|
2004
|
Non-RCT
|
Turkey
|
100
|
34
|
63/37
|
21/13
|
58.5±13
|
53±12.6
|
Kunisaki[21]
|
2006
|
Non-RCT
|
Japan
|
430
|
150
|
286/144
|
109/41
|
62.2±12.5
|
59.3±10.7
|
Yonemura[22]
|
2006
|
RCT
|
Japan
|
128
|
128
|
84/44
|
86/42
|
63.8 ± 9.7
|
62.5±10.2
|
Zhan [41]
|
2006
|
Non-RCT
|
China
|
146
|
126
|
92/34
|
113/33
|
NA
|
NA
|
Kulig [23]
|
2007
|
RCT
|
Poland
|
141
|
134
|
85/56
|
83/51
|
31-81
|
34-77
|
Sasako [25]
|
2008
|
RCT
|
Japan
|
263
|
260
|
176/87
|
183/77
|
25-75
|
25-75
|
Yonemura [24]
|
2008
|
RCT
|
Japan
|
135
|
134
|
90/45
|
91/43
|
63.8 ± 9.7
|
62.5±10.2
|
Hu [27]
|
2009
|
Non-RCT
|
China
|
55
|
62
|
42/13
|
48/14
|
58.8±11.4
|
54.3±11.4
|
HUANG [26]
|
2009
|
Non-RCT
|
China
|
101
|
50
|
77/24
|
35/15
|
52.3±11.2
|
52.6±12.5
|
Zheng [28]
|
2011
|
Non-RCT
|
China
|
33
|
42
|
19/14
|
29/13
|
53.5±11.2
|
55.9±8.9
|
Bostanci [29]
|
2013
|
Non-RCT
|
Turkey
|
370
|
98
|
248/122
|
61/37
|
60.2±12.4
|
56.2±11.9
|
liang [42]
|
2013
|
Non-RCT
|
China
|
109
|
44
|
72/37
|
25/19
|
NA
|
NA
|
SUN [43]
|
2013
|
Non-RCT
|
China
|
50
|
50
|
34/16
|
35/15
|
50.3±7.4
|
50.6±8.5
|
ZHANG [44]
|
2014
|
Non-RCT
|
China
|
88
|
69
|
NA
|
NA
|
NA
|
NA
|
zhang [45]
|
2015
|
Non-RCT
|
China
|
287
|
129
|
NA
|
NA
|
NA
|
NA
|
Marrelli [46]
|
2017
|
Non-RCT
|
Italy
|
353
|
390
|
NA
|
NA
|
NA
|
NA
|
RCTs adopt the Cochrane bias risk evaluation tool, which is edited by the Cochrane Collaborative network and is the first choice recommended by statisticians and system reviewers for evaluating RCT[30]. The evaluation results are shown in Figures 2 and 3. According to the bias risk charts, the following conclusions were obtained: (1) For random sequence generation (selection bias), 66.7% of RCTs had low risk and risk was unclear in 33.3% of RCTs. (2) For allocation concealment (selection bias), 33.3% of RCTs had low risk, risk was unclear in 50% of RCTs, and 16.7% of RCTs had high risk. (3) For performance bias, 66.7% of RCTs had low risk, and risk was unclear in 33.3% of RCTs. (4) For detection bias, 50% of RCTs had low risk and risk was unclear in 50% of RCTs. (5) For attrition bias, 100% of RCTs had low risk. (6) For reporting bias, 83.3% of RCTs had low risk and risk was unclear in 16.7% of RCTs. (7) For unclear risk of bias, the risk of other bias was unclear in 100% of RCTs.
nRCTs adopt the NOS scale for evaluation, and the higher the score, the better the quality[31]. The total score is 9. Specific rating is shown in Table 2.
Table 2
Newcastle-Ottawa Scale for assessing the quality of nRCTs
Study ID
|
|
Selection
|
Comparability
|
Outcome
|
Total score
|
|
Representativeness of the exposed cohort
|
Selection of the non- exposed cohort
|
Ascertainment of exposure
|
Demonstration that outcome of interest was not present at start of study
|
Comparability of cohorts on the basis of the design
|
Comparability of cohorts on the basis of the analysis
|
Assessment of outcome
|
Was follow-up long enough for outcomes to occur
|
Adequacy of follow up of cohorts
|
Ikeguchi [40]
|
2000
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
|
1
|
8
|
Yan-Chang [19]
|
2002
|
1
|
1
|
1
|
1
|
1
|
|
|
|
|
5
|
Bostanci [20]
|
2004
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
|
|
7
|
Kunisaki [21]
|
2006
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
9
|
zhan [41]
|
2006
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
9
|
Hu [27]
|
2009
|
1
|
1
|
1
|
1
|
1
|
|
1
|
1
|
1
|
8
|
HUANG [26]
|
2009
|
1
|
1
|
1
|
1
|
1
|
|
|
|
|
5
|
Zheng [28]
|
2011
|
1
|
1
|
1
|
1
|
1
|
|
|
|
|
5
|
Bostanci [29]
|
2013
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
9
|
liang [42]
|
2013
|
1
|
1
|
1
|
1
|
1
|
|
1
|
1
|
1
|
8
|
SUN [43]
|
2013
|
1
|
1
|
1
|
1
|
1
|
|
1
|
1
|
1
|
8
|
ZHANG [44]
|
2014
|
1
|
1
|
1
|
1
|
1
|
|
1
|
1
|
1
|
8
|
zhang [45]
|
2015
|
1
|
1
|
1
|
1
|
1
|
|
1
|
1
|
1
|
8
|
Marrelli [46]
|
2017
|
1
|
1
|
1
|
1
|
1
|
|
1
|
1
|
1
|
8
|
NOTE: Evaluating concerns of cohort study consists of the following three aspects: selection, comparability and outcome. A study can be awarded a maximum of one star for each numbered item.
|
3.3 Results of meta-analysis
(I) Operation time
Data of ten studies[17–19, 21, 22, 26, 27] were applicable. The meta-analysis results showed that MD = 99.45 min, 95%CI (48.93, 149.97), P < 0.001, and the differences between the two groups were statistically significant. Compared with the D2 group, the operation time in the D2+ group was longer with an average of 99.45 min (Figure 4).
(II) Intra-operative blood loss
Five studies[17, 19, 21, 22] reported intra-operative blood loss. The meta-analysis results showed that MD = 262.14 mL, 95%CI (165.21, 359.07). There was a significant difference between these two groups. Blood loss in the D2+ group was significantly more than that in the D2 group, and the test for heterogeneity test was 0.03 (Figure 5).
(III) Rate of post-operative complication
Fourteen studies[17–23, 25–29] mentioned the incidence of post-operative complications. The meta-analysis results showed that the post-operative complication rate in the D2+ group was higher than that in the D2 group [RR=1.42, 95%CI (1.11, 1.81), P<0.001] (Figure 6).
(IV) Post-operative mortality
Twelve studies [17–25, 27–29] mentioned post-operative mortality rate. The meta-analysis results showed that the differences between the two groups were not statistically significant. Compared with the D2 group, post-operative mortality of D2+ group was not increased [RR=0.96, 95%CI (0.59, 1.57), P=0.88] (Figure 7).
(V) Post-operative 5-year OS
Seven studies[17, 21, 24, 25, 27, 29] reported post-operative 5-year OS. The meta-analysis results showed that the differences between the two groups were not statistically significant. Compared with D2 surgery, D2+ surgery would not improve post-operative OS [HR=1.09, 95%CI (0.95, 1.25), P=0.22] (Figure 8).