Flow Diagram of the Studies Retrieved for the Review
All 77 articles were identified through electronic databased searching after filtration. Among them, 15 articles were duplicated, 27 articles were excluded because of unmatched titles and abstracts, 22 articles were excluded from reading full texts (because of inappropriate objects and incomplete data). The final 13 articles8–9, 11–21 included 3,690 CRC patients were selected to further meta-analysis. Figure 1 reveals the flowchart of study selection.
Baseline Characteristics of Included Studies
Table 1 summarizes the main characteristics of the eligible 13 studies. The analysis included 3,690 patients, ranging includes included 8 countries, from North America, Asia and Europe. All the specimens were tumor tissues after surgical resection. The most commonly used test method for F.nucleatum was quantitative polymerase chain reaction(qPCR),8, 12–15, 18–21 besides, three studies9, 11, 16 used the 16S ribosomal RNA(16sRNA) and Yuko Yamaoka used droplet digital PCR.17 All patients described in the retrieved articles were divided into two groups based on high or low expression of F.nucleatum DNA.
Association Between F.nucleatum Abundance And Prognosis Of Crc Patients
As the role of F.nucleatum in the prognosis of CRC patients is still controversial, we firstly analyzed the relationship between F.nucleatum abundance and prognosis of patients with CRC. Nine studies8–9, 12, 15–17, 19–21 reporting on a total of 2158 patients were selected for analysis of the association between abundance of F.nucleatum and OS.The fixed-effects model was adopted as a result of low heterogeneity. As shown in Fig. 2A, high abundance associated with worse OS in the patient with CRC (HR = 1.40, 95% CI: 1.40–1.63, P < 0.0001), without significant between-study heterogeneity (I2 = 0%, P = 0.80).
Moreover, data from five articles9, 14, 16, 18, 20 for a total of 1270 patients were selected for analysis of the association between the abundance of F.nucleatum and DFS. The fixed-effects model was applied as a result of low heterogeneity (I2 = 0%, P = 0.96). Our results demonstrated that the CRC patients with high abundance of F.nucleatum associated worse DFS than those with low abundance of F.nucleatum (HR = 1.71, 95% CI: 1.29–2.26, P = 0.0002)(Fig. 2B).
Last but not least, a total of 1498 patients in three studies8, 18, 21 were included to examine the relationship between the abundance of F.nucleatum and cancer-specific survival (CSS). In this analysis, F.nucleatum enrichment was significantly associated with poor CSS (HR = 1.93, 95% CI: 1.42–2.62 P < 0.0001) through the application of the fixed-effects model, with low heterogeneity (I2 = 0%, P = 0.69). (Fig. 2C)
Association Between high abundance of F.nucleatum and CRC Clinical Characteristics
As listed in Table 2, data from eleven articles8, 11–19, 21 for a total of 3413 patients were selected for analysis of the association between the abundance of F.nucleatum and primary tumor site in a random-effects model (I2 = 60%, P = 0.005). The result suggested that there is no significance evidence proving the correlation between F.nucleatum infection and tumor site (OR = 1.26, 95% CI: 0.91–1.75, P = 0.17) ( supplemental Fig. 1A).
A total of 3758 patients in nine studies8, 11–17, 21 were included to examine the relationship between the abundance of F.nucleatum and TNM stage (supplemental Fig. 1B). The F.nucleatum abundance was not associate with the overall TNM stage of CRC (OR = 1.20, 95% CI: 0.96–1.51, P = 0.11), with low heterogeneity (I2 = 25%, p = 0.22). However, high abundance of F.nucleatum was correlated with higher T (T3-T4) (OR = 2.20, 95% CI: 1.66–2.91, P < 0.00001) and M (M1) (OR = 2.11, 95% CI: 1.25–3.56, P = 0.005) stage respectively, without heterogeneity (I2 = 0%). And eight studies reporting on a total of 1445 patients revealed that F.nucleatum enrichment had no obvious correlation with N stage (OR = 1.27, 95% CI: 0.98–1.64, P = 0.07), with low heterogeneity (I2 = 37%) (supplemental Fig. 1C-E). Therefore, our result reveal that high abundance of F.nucleatum was associate with increasing of tumor size and distant metastasis in the CRC.
Furthermore, eight studies8, 11, 15–19, 21 reporting the association between the abundance of F.nuleatum and tumor differentiation with a total of 2118 patients were selected to analyze (supplemental Fig. 1F). As shown in Table 2, F.nuleatum enrichment was significantly associated with poor tumor differentiation (OR = 1.83, 95% CI: 1.11–3.03, P = 0.02) in CRC patient, with high heterogeneity (I2 = 60%).
Association Between high abundance of F.nucleatum and molecular characteristics in CRC
In order to further reveal the association between F.nucleatum infection and CRC progression, we analyzed the association between F.nucleatum enrichment and tumor-specific molecular characteristics. As shown in Table 3, our data from six studies8, 11–14, 21 demonstrated that high abundance of F.nucleatum were significantly associated with MSI-high type CRC (OR = 2.53, 95% CI: 1.53–4.20, P = 0.0003), although with high heterogeneity (I2 = 83%, P < 0.0001) (supplemental Fig. 2A). Interesting, the correlation between F.nucleatum enrichment and KRAS mutation was also found in fixed-effects model with low heterogeneity(I2 = 28%, p = 0.23) in six studies. 8,11−14, 17 The OR was 1.27 with a 95% CI of 1.00–1.61(P = 0.05) (supplemental Fig. 2B).
Moreover, six studies8, 11–14, 21 reporting on a total of 2499 patients were selected for analysis of the association between the abundance of F.nucleatum and BRAF mutation. Our result demonstrated that high abundance of F.nucleatum were not associate with BRAF mutation in CRC patient (OR = 1.93, 95% CI: 0.91–4.11, P = 0.09) (supplemental Fig. 2C). In addition, our pool result with three studies8, 17, 21 found that F.nucleatum enrichment in CRC tissue has no correlation with MLH1 hypermethylation (OR = 0.78, 95% CI: 0.06–9.93, P = 0.84) (supplemental Fig. 2D). At last, a total of 1603 patients in three studies8, 12, 13 were selected for analysis of the association between F.nucleatum enrichment and PIK3CA mutation through fixed-effect model, and there was no correlation between and PIK3CA mutation in CRC (OR = 1.21, 95% CI: 0.74–1.97, P = 0.45)( supplemental Fig. 2E).
Sensitivity Analysis
To evaluate the impact of a single study on the overall meta-analysis, included studies detecting F.nucleatum by qPCR or qrT-PCR were selected to perform sensitivity analysis (Table 4). The results of the sensitivity analysis are summarized in Table 4. The analysis of the studies using qPCR or qrT-PCR showed similar results to those of all studies together, including the relationship between F.nucleatum and Tumor side, TNM Stage, T stage, N stage, KRAS mutation, OS and DFS in CRC.
Risk Of Bias
The funnel plot were performed to assess publication bias. As shown in Fig. 3, the shape of funnel plots of main result was roughly symmetrical, without obvious evidence of asymmetry. The funnel plots for main outcomes, including OS, DFS and CSS, demonstrated no evidence of publication bias in our study.