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.