Increased expression of MCM5 is significantly associated with aggressive progression and poor prognosis of oral squamous cell carcinoma

Background Overexpression of MCM5 protein has been found to be significantly associated with the progression and prognosis of several human cancers. Methods This study used immunohistochemistry to examine the expression of MCM5 protein in 97 specimens of oral squamous cell carcinomas (OSCC), 80 specimens of oral epithelial dysplasia (OED, including 31 mild, 29 moderate, and 20 severe OED samples), and 20 specimens of normal oral mucosa (NOM). Results We found that the mean nuclear MCM5 labeling indices (LIs) increased significantly from NOM (15 +/- 6%), through mild (25 +/- 10%), moderate (34 +/- 9%), and severe OED (43 +/- 12%), to OSCC samples (61 +/- 16%, P<0.001). A significant correlation was found between the higher mean nuclear MCM5 LI and OSCCs with site at the tongue (P=0.046), larger tumor size (P=0.032), positive lymph node metastasis (P=0.003), more advanced clinical stage (P=0.002), higher histological grade (P=0.002), deeper invasion depth (P=0.0001), and perineural invasion (P=0.0047). Only nuclear MCM5 LI >= 60% was identified as independent unfavorable prognostic factor by multivariate regression analyses (P=0.049). The Kaplan-Meier curve showed that patients with OSCC with a nuclear MCM5 LI >= 60% had a significantly poorer cumulative survival than those with a nuclear MCM5 LI<60% (log-rank test, P=0.0062). Conclusions The increased expression of MCM5 protein begins at the oral pre-cancerous stage. The higher expression of MCM5 protein is significantly associated with the aggressive progression and poor prognosis of OSCC.