A total of 956 studies were identified in accordance with The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flow diagram (Fig.1). After removing 173 duplicates, 647 non-relevant studies were initially excluded by carefully screening the title and or abstract, and subsequently 109 articles were evaluated for eligibility via cautiously reviewing full-text and statistical data. Finally, 21 non-RCTs[4-9, 13-27] with 4871 patients were included in the quantitative Synthesis.
The details of these 21 comparative studies included in the meta-analysis are shown in Table 1. Among enrolled studies, 7 were performed laparoscopically and open surgery was operated in the other fourteen studies, of which 96.9% patients were pathologically diagnosed with stage I gastric cancer. Sixteen papers were reported by Japan, and only 5 studies were published by Korea and China.
Additional file 2 showed the analysis of demographic characteristics. The gender distribution in the PPG group were significantly different in both groups (OR=0.83, 95%CI=0.73–0.94, I2=0.00%, p=0.005), and no difference in articles compared age (WMD=0.19, 95%CI=-1.71–2.09, I2=87.90%, p =0.845) and BMI was demonstrated between two groups (WMD=-0.02, 95%CI=-0.24–0.19, I2=0.00%, p=0.828). What’s more, similar tumor size was observed in enrolled researches (WMD=0.02, 95%CI=-0.09–0.13, I2=31.50%, p=0.767). After quality assessment with nine-star Newcastle-Ottawa Scale, 18 reports which were identified as high-quality studies, were included in this meta-analysis and NOS scores were presented in Additional file 3.
Intraoperative and postoperative findings
Both procedures demonstrated comparatively results regarding operation time (WMD=-5.00, 95%CI=-13.53–3.54, I2=76.30%, p=0.251) (Fig. 2A) and blood loss (WMD=-19.85, 95%CI=-45.14–5.44, I2=74.90%, p=0.124) (Fig. 2B)between the PPG and DG group. However, we observed significantly fewer retrieved lymph nodes among the two groups (WMD=-1.10, 95%CI=-2.18–-0.01, I2=8.70%, p=0.048) (Fig. 2C), which was also found with the dissection or the preservation of No.5 lymph nodes. We also found longer hospital duration in PPG group (WMD=0.98, 95%CI=0.66–1.29, I2=30.60%, p=0.000) (Fig. 2D). However, the PPG group had a significantly shorter proximal resection margin and distal resection margin compared to DG group (WMD=-0.47, 95%CI=-0.91– -0.03, I2=74.30%, p=0.038; WMD=-2.76, 95%CI=-4.96–-0.57, I2=98.20%, p=0.013).
Morbidity and mortality
This meta-analysis demonstrated that there was no significant difference in the incidence of postoperative complications (OR=0.97, 95%CI=0.76–1.25, I2=5.70%, p=0.835) (Fig. 2E). According to anastomotic leakage, difference was found significant in PPG (OR=0.49, 95%CI=0.24–0.97, I2=0.00%, p=0.041) (Fig. 2F). In addition, there were significantly differences in delayed gastric emptying (OR=1.88, 95%CI=1.23–2.87, I2=38.40%, p=0.003) (Fig. 3A), which was also confirmed by assessing gastric emptying times (WMD=8.86, 95%CI=1.71–16.00, I2=0.00%, p=0.015).What’s more, PPG group revealed similar gallbladder stones rate (OR=0.63 95%CI=0.38–1.03, I2=14.60%, p=0.063) (Fig. 3B), but lower incidence of early dumping syndrome (OR=0.18, 95%CI=0.07–0.44, I2=0.00%, p=0.000). In terms of postoperative endoscopic findings and symptoms(Additional file 4), Patients performed with PPG procedure suffered fewer gastritis and bile regurgitation (OR=0.22, 95%CI=0.07–0.74, I2=71.30%, p=0.014; OR=0.30 95%CI=0.10–0.89, I2=57.90%, p=0.031), which was not found in esophagitis (OR=1.21, 95%CI=0.56–2.61, I2=37.90%, p=0.621).
Long-term oncological and nutritional outcomes
Discrepancy was not found on the overall survival rate described by three included studies (WMD=0.63, 95%CI=-0.06–1.32, I2=0.00%, p=0.074), and patients receiving PPG did not have a higher incidence of recurrence (OR=1.41, 95%CI=0.68–2.89, I2=0.00%, p=0.355) (Additional file 5). As shown in Figure 3, the serum total protein and albumin level in patients with PPG were higher compared with those with DG (SMD=0.39, 95%CI=0.25–0.53, I2=34.60%, p=0.000; SMD=0.31, 95%CI=0.17–0.44, I2=22.00%, p=0.000). Hemoglobin investigated in five articles showed better recovery (SMD=0.55, 95%CI=0.39–0.71, I2=0.00%, p=0.000). Moreover, PPG was found a better selection with fewer decreased body weight (WMD=3.24, 95%CI=1.79–4.69, I2=65.30%, p=0.000).
According to year of publication, study type and operation procedure, subgroup analysis was performed to explanation heterogeneity and evaluate the possible effect of these parameters (Table 3). Shorter operative time and less blood loss of PPG was only detected in the prospective studies. Significant differences were observed in gastritis in the retrospective studies, the studies with laparoscopic procedure and the studies before 2010. Delayed gastric emptying was associated with the retrospective studies, the studies with open surgery and the studies after 2010. What’s more, in terms of postoperative body weight change, we observe significant differences in all subgroup analysis
Sensitivity and Publication Bias
Possibility of publication bias was detected with constructing funnel plots and Egger’s linear regression test. We did not find significant publication bias expect for gastritis and body weight change (Fig. 4, Fig. 5 and Additional file 6). However, trim-and -fill test indicated the stability of this results. Furthermore, Galbraith plot was used to assess every individual study which account for the heterogeneity, and similar results were observed after exclusion of these researches in the supplemental information (Additional file 7,8,9).