Prognostic significance of Rab27 expression in solid cancer: a systematic review and meta-analysis

Rab27 is an essential molecule of vesicle fusion and trafficking in exosome secretion process, which plays important roles in cancer progression and metastasis. Recent studies reported that Rab27 expression is also associated with cancer prognosis. Therefore, we performed a meta-analysis to reveal the prognostic significance of Rab27 expression in solid cancer. Data were extracted by searching on PubMed, Embase and Cochrane library until February 15 2020. Pooled hazard ratio (HR) with confidence interval (CI) was calculated to evaluate the association between Rab27 expression and survival in solid cancer. Ten studies with 1434 cancer patients were including for this meta-analysis. High expression of Rab27 was associated with poor survival (HR 2.67, 95% CI 1.52–4.69, p = 0.001). High expression of Rab27A was significantly associated with lymph node metastasis (HR 1.53, 95% CI 1.00–2.34, p = 0.048). High expression of Rab27B was significantly correlated with lymph node and distant metastasis (HR 2.15, 95% CI 1.56–2.95, p < 0.001; HR 6.80, 95% CI 3.12–14.85, p < 0.001), and higher TNM stage (HR 2.55, 95% CI 1.78–3.65, p < 0.001). This meta-analysis revealed that Rab27 expression could be a potential prognostic marker in solid cancer.

www.nature.com/scientificreports/ The included studies were consisted of seven types of cancers, including renal cell carcinoma (n = 1), lung cancer (n = 2), ovarian cancer (n = 1), pancreatic cancer (n = 2), colorectal cancer (n = 2), breast cancer (n = 1), and hepatocellular carcinoma (n = 1). All studies performed immunohistochemistry to evaluate Rab27A or Rab27B expression in the human cancer tissue, and the majority of the cut-off value were scoring system using staining intensity and proportion. The Newcastle-Ottawa Scale (NOS) score is 7 to 8, which is considered to be high quality studies.
Association between Rab27 expression and clinicopathological characteristics. Analysis of the association between Rab27 expression and clinicopathological characteristics of cancer patients was summarized in Table 3. The results suggested that high expression of Rab27A was significantly associated with lymph node metastasis (HR 1.53, 95% CI 1.00-2.34, p = 0.048) (Fig. 4A). However, there was no significant relationship between Rab27A expression with age, gender, tumor grade and stage, distant metastasis, and TNM stage ( Fig. 4B-G).
Publication bias and sensitivity analysis. Visual inspection of the Funnel plot revealed asymmetry ( Fig. 6A). This suggests the possibility of a visual bias in publishing, however the Egger's test was not statistically significant (p = 0.849). Thus, the trim and fill method was applied. The results showed the significant association between Rab27 expression with survival (HR 1.85, 95% CI 1.02-3.36, p = 0.042) (Fig. 6B). The sensitivity analysis was conducted to verify the reliability of our results. The pooled HR for survival was not influenced after one by one, excluding each study, indicating our results are consistent and credible (HR 2.62, 95% CI 2.02-3.40) (Fig. 7).

Discussion
The Rab family members are key regulators that involve in the replacement of substances in the various stages of vesicular trafficking 17 . Rab27 is a valuable member in Rab family and contains Rab27A and Rab27B, which share 70% sequence identity of the amino acid level 17,22 . Rab27 is located on the membrane-bound compartments and takes part in the docking multivesicular endosomes, which is known to control exosome secretion 17,29,30 .  6 . Moreover, Rab27 has been revealed to function a critical role in the proliferation and invasion of cancer cells by the controlling of exosome secretion, which modulates the tumor microenvironment and the function of cancer cell 6    www.nature.com/scientificreports/ www.nature.com/scientificreports/ studies have reported that Rab27 expression is associated with the prognosis of cancer 8,20-28 . Thus, we evaluated that the association between Rab27A expression and survival. This meta-analysis of 10 studies including 1434 patients assessing the prognostic significance of Rab27 expression in solid cancer revealed that high expression of Rab27 was a potential prognostic marker for poor survival in cancer patients.
In the subgroup analysis of cancer type, poor survival was related to Rab27 expression in lung cancer and pancreatic cancer without heterogeneity. On the other hand, survival was not significantly correlated with Rab27 expression in colorectal cancer. This seems to be due to the conflicting results of the two studies in this group. Thus, additional research is needed in colorectal cancer. Regarding the subgroup of sample size and survival www.nature.com/scientificreports/ outcomes, poor survival was correlated to Rab27 expression in both groups, respectively. As showed in Fig. 3D, poor survival was significantly associated with high expression of Rab27B, but not with Rab27A. This seems to be due to the study of Shi et al. that reported high expression of Rab27A indicates favorable prognosis showing contrary results with other studies. With regard to the clinicopathological characteristics, our analysis revealed that high expression of Rab27 was significantly correlated with lymph node metastasis. Moreover, Rab27B was also significantly associated with distant metastasis and TNM stage. This results strongly suggests that high expression of Rab27 is related to the prognosis of cancer patients.
This meta-analysis has the following limitations. First, all included studies originated from Asia, which may lead to our results not reflecting western countries. Second, cancer type and sample size were small, undermining the credibility of our results. Third, the discrepancy of cut-off value determining Rab27A and Rab27B expression may affect our results. However, we demonstrated a comprehensive analysis of the association between Rab27A and Rab27B expression with survival in solid cancer. To the best of our knowledge, this meta-analysis is the first report to systematically evaluate the association between Rab27 expression with survival in solid cancer.
In conclusion, this systematic review and meta-analysis revealed that Rab27 expression could be a prognostic marker in solid cancer.

Methods
Search strategy and selection criteria. We searched the PubMed, Embase and Cochrane library until February 15 2020 using the following terms: (Rab27A or Rab27B) and (cancer or tumor or carcinoma or neoplasm or malignancy) and (prognostic or predict or prognosis or survival or outcome). We reviewed all significant publications in the references of the articles.
The inclusion criteria were: (1) Rab27A or Rab27B was detected in the human cancer tissue, which diagnosed by pathologic examination; (2) the association between Rab27A or Rab27B and survival outcomes was reported; (3) the HR and 95% CI for survival outcomes were provided.
The exclusion criteria were: (1) duplicate studies; (2) conference abstracts, case reports, reviews, letters, and non-English articles; (3) preclinical studies, such as laboratorial or in vitro studies. Data extraction. Two authors independently collected the following data from the included studies: first author, year of publication, country, cancer type, sample size, clinicopathological characteristics, study period, follow-up period, survival outcomes, Rab27 associated with prognosis, cut-off value of Rab27 expression, and survival data. When there was a disagreement, we reached an agreement through discussion. www.nature.com/scientificreports/ www.nature.com/scientificreports/ www.nature.com/scientificreports/ Quality assessment. Two authors independently evaluated the quality of included studies by the NOS. The NOS scores ranged from 0 to 9. The studies with NOS scores of greater than 6 were regarded as a high quality.
Cochran's Q and I 2 statistics were used to assess the heterogeneity among the included studies. An I 2 > 50% or a p value < 0.1 was considered as statistically significant in a random-effects model. Pooled HR and 95% CI were calculated for evaluating the prognostic significance of Rab27 expression. Subgroup analysis was performed to assess the source of heterogeneity. Funnel plot and Egger's test were also performed to evaluate the publication bias. And the sensitivity analysis was applied to assess the reliability of the pooled results. A p value < 0.05 was regarded as statistically significant. www.nature.com/scientificreports/