Search results and baseline detailsFig. 1

Flowchart for extracting relevant articles from literature

Based on the established retrieval strategy and by merging potential reference lists from pending articles, we initially obtained 108 articles. After a preliminary review of the titles and abstracts, we excluded 69 articles due to reasons such as duplication, irrelevant types, and mismatched study subjects. Subsequently, we thoroughly reviewed the full texts of 39 articles and further excluded 20 of them (excluded for database analyses and bioinformatics research [n = 11], incorrect cancer types [n = 4], meta-analyses [n = 4], and lack of survival data [n = 1]). Ultimately, 19 eligible articles, comprising 20 distinct studies, were included in this meta-analysis (Fig. 1). These retrospective studies, conducted in Italy [10, 13], Japan [3, 14, 15], Turkey [16,17,18], Spain [19], China [20,21,22,23,24,25,26,27,28], and Korea [29], were published between 2020 and 2024 and included six types of digestive system cancers: colorectal cancer, esophageal cancer, gastric cancer, hepatocellular cancer, oral cavity cancer, and pancreatic cancer. The studies collectively included 5037 patients who received surgery, chemotherapy, targeted therapy, immunotherapy, or radiotherapy between 2000 and 2023. The number of patients in each study ranged from 51 to 853, and they were divided into two groups based on a certain pre-treatment PIV cutoff value. Sixteen studies provided prognostic data on overall survival (OS), five studies on progression-free survival (PFS), five studies on disease-free survival (DFS), two studies on recurrence-free survival (RFS), and two studies on cancer-specific survival (CSS). Of these, 16 studies estimated hazard ratios (HR) through univariate analysis, while 14 studies did so through multivariate analysis. Notably, based on the NOS scores, all included articles were considered high-quality studies. Refer to Table 1 for more information.

Table 1 Main characteristics of studies included in meta-analysisRelationship between PIV and the prognosis of patients with digestive system cancersFig. 2

Forest plot of overall survival in patients with digestive system cancers based on PIV levels

Fig. 3

Forest plots of survival outcomes: (a) progression-free survival, (b) disease-free survival, (c) recurrence-free Survival, and (d) cancer-specific survival by PIV levels

Through meta-analysis, we confirmed that high PIV levels were associated with poor prognosis in patients with digestive system cancers, as shown in Figs. 2 and 3. Specifically, our meta-analysis, which included 16 studies, revealed that patients with high PIV levels had shorter OS compared to those with lower PIV levels (HR = 2.039, 95% CI = 1.630–2.550, P < 0.001, Fig. 2). Additionally, the results demonstrated that high PIV levels were adverse factors for PFS (HR = 1.877, 95% CI = 1.069–3.295, P = 0.028, Fig. 3a) and DFS (HR = 1.624, 95% CI = 1.155–2.285, P = 0.005, Fig. 3b) in the pooled analysis of five studies each. Furthermore, combined analysis on RFS (HR = 2.393, 95% CI = 1.052–5.442, P = 0.037, Fig. 3c) and CSS (HR = 2.053, 95% CI = 1.548–2.723, P < 0.001, Fig. 3d) also confirmed the association between high PIV levels and poor patient outcome.

According to the results of the chi-square test and I2 statistic, we found significant heterogeneity in all prognostic analyses except for the comprehensive analysis of the impact of PIV on patient CSS. Since studies on OS were predominant, we further analyzed possible sources of its high heterogeneity (I2 = 79.4%, Ph < 0.001). However, based on the meta-regression results, we did not confirm significant sources of heterogeneity. The P-values for cancer type (P = 0.765), sampling time (P = 0.436), cutoff value (P = 0.240), analysis method (P = 0.523), treatment strategy (P = 0.488), study region (P = 0.958), and sample size (P = 0.081) were all greater than 0.05.

Subgroup analyses for correlation between PIV and OS

Due to the majority of included articles substantiating the relationship between PIV and OS, we conducted a subgroup analysis to further explore the prognostic value of PIV on OS in patients with digestive system cancers. The results were summarized in Table 2. From the subgroup analysis, we observed that patients with high PIV had significantly shortened OS across various cancer types subgroups, including digestive tract cancer (HR = 1.689, 95% CI = 1.504–1.896, P < 0.001), colorectal cancer (HR = 2.178, 95% CI = 1.786–2.657, P < 0.001), esophageal cancer (HR = 1.656, 95% CI = 1.373–1.996, P < 0.001), and hepatobiliary pancreatic cancer (HR = 2.427, 95% CI = 1.581–3.727, P < 0.001). We also confirmed the adverse prognostic impact of high PIV across different analysis method subgroups (Multivariate analysis, HR = 2.076, 95% CI = 1.578–2.732, P < 0.001; Univariate analysis, HR = 2.630, 95% CI = 1.700-4.068, P < 0.001). Furthermore, we analyzed the timing of blood sample collection, cutoff values for PIV, and sample size. Our findings indicate that under a well-designed study framework, variations in sampling time (Within 1 week before treatment, HR = 1.960, 95% CI = 1.411–2.724, P < 0.001; Before treatment, HR = 2.042, 95% CI = 1.539–2.708, P < 0.001), differences in PIV cutoff values (< 300, HR = 1.631, 95% CI = 1.304–2.039, P < 0.001; ≥ 300, HR = 2.692, 95% CI = 2.466–2.937, P < 0.001), and the size of the study sample (< 300, HR = 2.741, 95% CI = 2.505–2.999, P < 0.001; ≥ 300, HR = 1.686, 95% CI = 1.359–2.092, P < 0.001) did not affect the analytical results. Similarly, subgroup analyses based on different treatment strategies demonstrated that PIV had predictive value in patients undergoing both surgical (HR = 1.885, 95% CI = 1.484–2.394, P < 0.001) and non-surgical (HR = 2.237, 95% CI = 1.656–3.023, P < 0.001) treatments. Additionally, studies conducted in various regions (East Asia, HR = 1.828, 95% CI = 1.450–2.304, P < 0.001; Other region, HR = 2.230, 95% CI = 1.723–2.887, P < 0.001) consistently showed that high PIV levels led to reduced survival times in patients with digestive system cancers.

Table 2 Subgroup analyses of PIV and OS in digestive system cancersAssessment of the stability and publication biasFig. 4

Sensitivity analysis of overall survival in cancer patients

Fig. 5

Evaluation of publication bias in included studies using egger’s test

To deepen our understanding of the stability of meta-analysis regarding the impact of PIV on OS in patients with digestive system cancers, we conducted additional sensitivity analysis. The results indicated that all estimated points fall within the 95% CI (Fig. 4), confirming the stability of this analysis. Furthermore, Begg’s (P = 0.065) and Egger’s (P = 0.258, Fig. 5) tests confirmed the absence of publication bias in this analysis.