Relation between outcomes and localisation of p-mTOR expression in gastric cancer

The mammalian target of rapamycin (mTOR), a Ser/Thr protein kinase that mediates intracellular signalling related to cell growth, proliferation, and differentiation, has received considerable interest as a possible target for cancer treatment. We evaluated the correlation of mTOR expression with clinicopathological features, outcomes, and the expression of Akt, an upstream regulator of mTOR, in gastric cancer. Tumour samples were obtained from 109 patients with gastric adenocarcinomas who underwent a radical gastrectomy. The expressions of phosphorylated mTOR (p-mTOR) and phosphorylated Akt (p-Akt) in the cytoplasm and in the nucleus were analysed by immunohistochemical staining. Cytoplasmic p-mTOR expression positively correlated with the depth of tumour invasion (T1 vs T2–4, P=0.003), involved lymph nodes (P=0.010), and tumour stage (I vs II–IV, P=0.002). In contrast, nuclear p-mTOR expression negatively correlated with these variables (P<0.001,=0.035, and <0.001). Cytoplasmic p-mTOR expression was associated with significantly poorer relapse-free survival (RFS, P=0.037) and overall survival (OS, P=0.024), whereas nuclear p-mTOR expression was associated with better RFS and OS (P=0.029, 0.059). Neither cytoplasmic nor nuclear p-Akt expression was associated with any clinicopathological factor or with survival. Localisation of p-mTOR may play an important role in tumour progression and outcomes in patients with gastric cancer.