Phosphorylated ribosomal protein S6 correlation with p21 expression and inverse association with tumor size in oral squamous cell carcinoma

Background The purpose of this study was to investigate the clinical relevance of phosphorylated ribosomal protein S6 (p‐S6), a surrogate marker of mammalian target of rapamycin (mTOR) activation, and p21 in a series of 125 patients with oral squamous cell carcinomas (OSCCs). Methods Immunohistochemical analysis was performed to ascertain the phosphorylation status of p‐S6 at Ser235/236 and Ser240/244, p21, and p53 protein expression. Results Expression of phosphorylated S6 protein on either serine 235/236 or serine 240/244 was detected in 83% and 88% tumors, respectively, and both of them were inversely and significantly correlated with the tumor size and local infiltration. Positive p21 expression was found in 91.5% of the cases, and was inversely correlated with tumor size. In OSCC, p21 expression correlates with p‐S6 levels, a surrogate marker of mTOR activation, independently of p53 status. Conclusion Expression of both p21 and p‐S6 was found to inversely associate with tumor size but not survival outcomes in patients with OSCC.