1 Introduction
Oral squamous cell carcinoma (OSCC) is the most commonly diagnosed oral
cancer, which accounts for approximately 90% of all malignant oral
neoplasm1. Programmed cell death ligand-1 (PD-L1) is a
surface glycoprotein of cancer cells, which is regarded as the
inhibitory receptor programmed cell death-protein 1 (PD-1) on T
lymphocytes2. PD-L1 involves in the immune response
evasion by binding to PD-1 that downregulates T-cell responses.
As one of the most common immunologic checkpoints, the axis PD-1/PD-L1
has showed prognostic significance that mediates immune tolerance.
Accompanied by the increasing number of researches finding that
activation of immune checkpoint blockade is effective in tumour growth
control and survival extension, controversy has also been persistent due
to non‐homogeneous conclusions. Several studies approved of either
positive3,4[4, 5], or negative association of
PD-L1 overexpression with prognosis5,6, while other
studies showed no prognostic significance of PD-L1
expression7,8.
Inconsistent results were mainly presumed to be related to the various
methods for immunohistochemical staining, stage of diagnosis, tumor
location, and the feasibility of radical surgical
resection9. The previous meta-analyses reached a
consensus that PD-L1expression in OSCC patients was not significantly
correlated with overall survival (OS), but major limitation of them did
not consider oral subsites or immunostaining patterns as confounding
factors.
To date, the role of PD-L1 expression in OSCC of tongue has attracted
attention of the increasing number of studies. It was reported that high
PD-L1 expression was associated with worse OS that was exclusively found
in OSCC of the tongue. However, the prognostic significance of PD-L1
expression was not observed in oropharyngeal
carcinomas10. To find the discrepancy complicated by
the use of different immunostaining patterns, comparison was conducted
stratified by various scoring systems, antibodies clone. One study
indicated that no relationship between PD-L1 expression and survival was
found by using either combined positive score (CPS) or tumour proportion
score (TPS)9. In contrast, other reports have found
high PD-L1 expression was linking to better prognosis when cut off of ≥
5% of TPS and ≥ 1 of CPS11. A recent approach
assessed PD-L1 expression measured by two different anti-PD-L1
antibodies (22C3, E1LN3), and revealed that high PD-L1 expression
detected by 22C3 presented a worse prognosis in terms of
disease-specific survival (DSS)12.
Therefore, it was appropriate for performing a meta-analysis to
determine whether the prognostic significances of PD-L1 expression in
OSCC differed by oral compartments and methods for PD-L1 immunostaining.