Figure 3. Sensitivity analysis chart after excluding individual studies.
Discussion
The role of preoperative PLR in predicting prognosis in patients with laryngeal cancer had been investigated in several articles, but their effects were inconsistent and uncertain. We, therefore, analyzed the data from these articles in hope for obtaining more comprehensive of the value of preoperative PLR for laryngeal cancer. Our analysis, which combined the results of 1,711 patients from 7 studies, showed that higher PLR levels was correlation with poorer OS (HR: 1.70, 95%CI 1.71-2061, p<0.001). The result of subgroup analyses showed that increased PLR was associated with poorer OS in different treatment including surgical or with concurrent chemoradiotherapy. Meanwhile, higher PLR was an important negative prognostic marker when cut-off value >114.
Multiples studies had demonstrated that PLR is a marker of worse prognosis in kinds of tumors, like hepatocellular carcinoma, gastric carcinoma, Colorectal tumor, ovarian tumor, kidney tumor and non-small cell lung cancer, with the exception of pancreatic cancer. As for head and neck tumor, it had been shown that NLR was a prognostic marker in nasopharyngeal carcinoma, but PLR had not been found to have the same effect.
It had been shown that inflammation had correlation with occurrence and advancement of tumors [22]. People infected with hepatitis B virus were more likely to progress to hepatocellular carcinoma, in addition helicobacter pylori infection is related to an increased risk of gastric cancer [23]. Neutrophils in TME (tumor microenvironment), would discharge ROS, NO, VEGF, chemokines, and other materials that interact with TAM, MDSC and mononuclear cells. These cells could impede T cell gathering and exerted immune function, they could also boost tumor progression[24]. Platelets could also mediate the growth, proliferation and angiogenesis of tumor cells. If platelets were activated, by direct or indirect contact, they could help tumor cell survival and progression [25, 26]。Moreover, Platelets and tumor cells could form a complex to help tumor cells escape from immune killing. Motivated platelet could secret TGF-β and VEGF, it could also inhibit NK cells, ultimately promote tumor progression and metastasis[30, 31]. Lymphocytes were responsible for immune monitoring and thus eliminating tumor cells. In a variety of tumors, reduced peripheral blood lymphocyte number was associated with poor prognosis[27, 28]. It had been found that cancer cells could elevate the number of peripheral platelets by thrombocytopenia, IL-6, or leukemia suppressor [29]. Elevated PLR indicated an increase in platelet count and a decrease in lymphocyte count, it could increase the risk of tumor recurrence and metastasis.
This meta-analysis also had limitations that need to be fully discussed. First of all, there was significant heterogeneity in calculation the HR values for OS of the included articles (I2=81.8%, P=0.000). Despite the use of sensitivity analysis and meta-regression, the source of heterogeneity had not been completely found. The second limitation of this analysis was that the number of literatures included was small and they were all retrospective studies. The current form of research was literature-based analysis, which leads to the marginal significance of publication bias in HR to OS. Part of the potential publication bias may be due to the tendency of publications to produce positive results; At the same time, this may be the result of relatively strict standards of inclusion. The PLR cutoff values for each center were defined inconsistently. Therefore, there was an urgent need to establish standard and uniform PLR cut-off values. In order to achieve more meaningful results, further investigation of the PLR cut-off point was required. Fewer than 10 references were included in this meta-analysis, Egger’s and Begg’s test had a relatively low effect. Therefore, Egger’s and Begg’s test could not detect the publication bias. The third, only English articles were included in this analysis, so publication bias could not be excluded.
Conclusion
This meta-analysis suggested that improved PLR may be a negative outcome for patients with laryngeal cancer. More randomized controlled trials and large-scale studies were needed to confirm this conclusion.
Ethical approval: This article does not contain any studies with human participants or animals performed by any of the authors.