Introduction:
Myeloid-Derived Suppressor Cell (MDSC) is critically involved in cancer immune suppression and its density has been recognized as a robust prognostic biomarker. Here, we sought to characterize the densities and locations of CD11b+ MDSCs in primary oral squamous cell carcinoma (OSCC) and determine their prognostic significance.

Material and methods:
A total number of 144 eligible OSCC samples from a tertiary referral oral cancer center were retrospectively collected. Intensities of CD11b+ MDSCs at tumor center (CT) and invasive margin (IM) in OSCC samples were detected by immunohistochemistry and automatically quantified using Image J software. The optimal cutoff values for CD11b CT and CD11b IM were determined by X-tile based on overall survival. The associations between CD11b+ MDSCs and clinicopathological parameters were assessed by the Chi-square test. The prognostic value of CD11b+ MDSCs was evaluated by Kaplan-Meier plots, Cox regression analyses and receiver operating characteristics curves.

Results:
High density of CD11b+ MDSCs at CT or IM significantly associated with inferior overall and disease-free survival (Kaplan-Meir, P < 0.05, Log-rank test). CD11b CT and CD11b IM were identified as independent prognostic predictors for patient survival. The prediction accuracy and specificity of CD11b CT and CD11b IM were superior to other prognostic parameters.

Conclusions:
Our data indicated that increased densities of CD11b+ MDSCs at CT and IM regions significantly associated with poor prognoses which might be novel prognostic factors for OSCC.