Co-expression of CMTM6 and PD-L1: a novel prognostic indicator of gastric cancer

BACKGROUND: CKLF Like MARVEL Transmembrane Domain Containing 6 (CMTM6) is involved in the epigenetic regulation of genes and tumorigenesis. Programmed cell death ligand 1 (PD-L1) is closely related to the prognosis of some human cancers. CMTM6 is a key regulator of PD-L1 in many cancers. The purpose of this study was to investigate the expressions of these proteins in gastric cancer and the correlations with clinicopathological features and survival. METHODS: The expression levels of CMTM6 and PD-L1 were examined in 185 gastric cancer specimens using immunohistochemistry, quantitative real-time PCR and Western blot. Immunofluorescence was used to examine the localizations of CMTM6 and PD-L1. Chi-square test was used to analyze the relationship between CMTM6 and PD-L1 expressions and clinicopathological characteristics. Kaplan–Meier method and log-rank test were used to analyze the survival data of patients. RESULTS: The positive expression rates of CMTM6 and PD-L1 in gastric cancers were 78.38% (145/185) and 75.68% (140/185), respectively. CMTM6 and PD-L1 were both mainly expressed in the cell membrane and nucleus of gastric cancer tumor cells. High expression of CMTM6 and PD-L1 was correlated with Borrmann type (P < 0.001), N stage (P = 0.002), peritoneal metastasis (P = 0.007) and TNM stage (P = 0.038). CMTM6 and PD-L1 expression in gastric cancer tissues showed a positive correlation (Pearson’s coefficient test, r = 0.260; P < 0.001). CMTM6 may positively regulate PD-L1 expression. High expression of CMTM6 was correlated with poor prognosis of gastric cancer patients (HR = 1.668; 95% CI = 1.032–2.695; P = 0.037). High expression of both CMTM6 and PD-L1 may be an independent factor for overall survival (HR = 1.554; 95% CI = 1.011–2.389; P = 0.044). CONCLUSION: The combined detection of CMTM6 and PD-L1 may be used as an indicator for judging the prognosis of gastric cancer patients.