Phosphorylation of p70S6 kinase predicts overall survival in patients with clear margin-resected hepatocellular carcinoma

The mammalian target of rapamycin (mTOR) inhibitors play a key role in regulating signal transduction by blocking the mTOR pathway and combining anticancer and immunosuppressive properties. This study was undertaken to determine the prevalence and clinicopathological relevance of phospho-p70S6 (p-p70S6) kinase in hepatocellular carcinoma (HCC) and to investigate the effects of rapamycin on HCC in vitro. A total of 196 patients with HCCs were treated either with surgical resection (n=106) or liver transplantation (n=90). Tumour tissue was investigated for p-p70S6, phospho-AKT, Ki-67, Cyclin-D1 and apoptosis, and staining results were correlated with clinicopathologically relevant parameters. Overall, p-p70S6 was detected in 24.5% (48/196) of HCCs. In the resection group, 26.4% (28/106) of HCC were positive and 22.2% (20/90) in the transplant group. p-p70S6 was significantly associated with elevated Cyclin-D1 immunoexpression and was correlated with decreased overall survival (P=0.011) in patients resected with a clear margin. In multivariate COX regression analysis, p-p70S6 was identified as an independent prognostic parameter in patients resected with a clear margin. Rapamycin induced apoptosis and growth inhibition by G0/G1 cell cycle arrest in vitro. However, in HCC patients p-p70S6 kinase was not associated with proliferation or apoptosis. Activation of p70S6 kinase indicates aggressive tumour behaviour in patients with clear margin-resected HCC. Identification of p-p70S6 kinase in HCC selects high-risk patients who may benefit from drugs targeting the mTOR pathway.