The number of potentially relevant studies identified through the literature search across four databases was 4880, and after automatic deduplication, 3268 articles were identified as the only literature. After reading the titles and abstracts of the 3268 articles, 3254 were ruled ineligible, leaving 14 articles to be reviewed in full text. Five studies were disqualified because of a literature review or insufficient data; a lack of data led to the exclusion of one protocol study, and three studies were abstracts from conferences. Manually searching the reference lists did not yield any additional studies. There were only five studies [16, 17, 20,21,22] that satisfied all of the inclusion criteria set by this meta-analysis, so only those results were used. The entire systematic literature review is shown in Fig. 1.

PRISMA selection flow diagram

Table 1 provides detailed information on the five studies included in this study. These five studies [16, 20,21,22,23], published between 2018 and 2021, included 1171 patients with LAGC who were treated with surgery after NCT from 2006 to October 2018. The NCT regimens included S-1 and oxaliplatin (SOX); epirubicin, oxaliplatin, and capecitabine (EOX); capecitabine and oxaliplatin (XELOX); epirubicin, cisplatin, and 5-FU (ECF); docetaxel, oxaliplatin, leucovorin, and 5-fluoracil (FLOT); fluoropyrimidine- and platinum-based doublet (FP); epirubicin, cisplatin, and capecitabine (ECX); and other chemotherapy regimens. The five studies differed in their TTS groupings. Three studies [17, 20, 22] examined three TTS, including > 6 weeks, 4–6 weeks, and < 4 weeks. In one study [16], TTS was divided into ≥ 43 days, 31–42 days, and ≤ 30 days. Patients whose TTS ≥ 43 days, 31–42 days, and ≤ 30 days were classified as belonging to the > 6 weeks, 4–6 weeks, and < 4 weeks, respectively, for the purposes of data analysis. In another study [21], TTS was divided into ≤ 21 days, 22–28 days, 29–35 days, 36–42 days, and 43–84 days. Likewise, TTS ≤ 21 days and 22–28 days combined were considered < 4 weeks, TTS 29–35 days and 36–42 days combined were considered 4–6 weeks, and TTS 43–84 days were considered > 6 weeks. Therefore, the number of patients included in the analysis was 411 with TTS < 4 weeks, 507 with TTS 4–6 weeks, and 253 with TTS > 6 weeks. Based on the NOS assessment [19], five studies were reviewed, with four receiving seven stars (showing high quality) and one receiving eight stars (also indicating high quality).

The overall survival outcomes were reported in all five studies [16, 17, 20,21,22]. According to the study’s findings, in terms of overall survival outcomes, no statistically significant differences were found among < 4 weeks and 4–6 weeks (HR 1.04, 95% CI: 0.69–1.57, and P = 0.85) and > 6 weeks (HR 0.83, 95% CI: 0.52–1.33, and P = 0.44). There was a significant decline in overall survival associated with > 6 weeks when compared to 4–6 weeks (HR 1.34, 95% CI: 1.03–1.75, and P = 0.03) and no significant heterogeneity (I2 = 0%, P = 0.48). Figure 2 demonstrates these results.

Overall survival (OS). A < 4 weeks vs. 4–6 weeks. B < 4 weeks vs. > 6 weeks. C > 6 weeks vs. 4–6 weeks

DFS was noted in four studies [16, 17, 20, 21], and 393 individuals with TTS < 4 weeks, 481 individuals with TTS 4–6 weeks, and 237 individuals with TTS > 6 weeks were ultimately incorporated into the analysis.

The final study revealed that the HR values for DFS were 0.96 (< 4 weeks vs. 4–6 weeks, 95% CI: 0.77–1.20 and P = 0.73), 0.88 (< 4 weeks vs. > 6 weeks, 95% CI: 0.51–1.51, and P = 0.64), and 1.13 (> 6 weeks vs. 4–6 weeks, 95% CI: 0.73–1.75, and P = 0.58), respectively. There were no statistically significant differences between the comparison groups. These outcomes are displayed in Fig. 3.

Disease-free survival (DFS). A < 4 weeks vs. 4–6 weeks. B < 4 weeks vs. > 6 weeks. C > 6 weeks vs. 4–6 weeks

Pathological complete response (pCR) data from four of the five studies were published [17, 20,21,22], and all of the studies included evaluations of curative effects according to RECIST1.1 [24]. According to the results of the final analysis, the odds ratio (OR) values for pCR were 1.24 (< 4 weeks vs. 4–6 weeks, 95% CI: 0.72–2.14, and P = 0.44), 0.61 (< 4 weeks vs. > 6 weeks, 95% CI: 0.32–1.15, and P = 0.13), and 1.70 (> 6 weeks vs. 4–6 weeks, 95% CI: 0.93–3.31, and P = 0.09), respectively. The comparative groups did not differ significantly from one another. These outcomes are shown in Fig. 4.

Pathological complete response (pCR). A < 4 weeks vs. 4–6 weeks. B < 4 weeks vs. > 6 weeks. C > 6 weeks vs. 4–6 weeks

Data on the pathologic response were reported in three of the five studies [16, 20, 22]. One of the studies [16] evaluated the curative effect according to Becker et al. [25], which was excluded from the pooled analysis. The other two articles [20, 22] used RECIST1.1 [24], and the analysis results suggested that the OR values for mPR were 1.21 (< 4 weeks vs. 4–6 weeks, 95% CI: 0.68–2.17, and P = 0.51), 0.99 (< 4 weeks vs. > 6 weeks, 95% CI: 0.50–1.94, and P = 0.97), and 1.22 (> 6 weeks vs. 4–6 weeks, 95% CI: 0.66–2.27, and P = 0.52), respectively. The comparative groups did not differ significantly from one another. These outcomes are displayed in Fig. 5.

Major pathologic response (mPR). A < 4 weeks vs. 4–6 weeks. B < 4 weeks vs. > 6 weeks. C > 6 weeks vs. 4–6 weeks

A total of 36.74% of patients (187/509) experienced postoperative complications according to two papers on postoperative complications [16, 20]. The findings of the final analysis show that OR for postoperative complications was 0.84 (< 4 weeks vs. 4–6 weeks, 95% CI: 0.54–1.30, and P = 0.42), 0.90 (< 4 weeks vs. > 6 weeks, 95% CI: 0.54–1.49, and P = 0.67), and 0.93 (> 6 weeks vs. 4–6 weeks, 95% CI: 0.59–1.45, and P = 0.74), respectively. The comparative groups did not differ significantly from one another. These results are shown in Fig. 6.

Postoperative complications. A < 4 weeks vs. 4–6 weeks. B < 4 weeks vs. > 6 weeks. C > 6 weeks vs. 4–6 weeks