**4. Mammalian target of rapamycin (mTOR) signalling pathway**

This pathway is a critical regulator of numerous physiological processes and also plays a pivotal role in cell proliferation and metastasis of transformed human cancers including HCC. It is upregulated in around 40% of HCC and has been associated to poor prognosis and early recurrence independent of underlying liver aetiology [35]. Two mTOR inhibitors have been studied in clinical trials.

Preclinical studies have shown everolimus (taken orally) to dose-dependently inhibit tumour growth in patient-derived xenograft models of advanced HCC [36]. In a phase I/II study (NCT00516165) in advanced HCC patients, Zhu et al. [37] reported daily dose of 10 mg per day to be well tolerated in 28 patients producing a medium PFS and OS of 3.8 months and 8.4 months respectively. The subsequent phase II study involving 28 patients with prior systemic therapy with daily dose of 10 mg could not be completed as two patients remained progression free for 24 weeks. Although everolimus was well tolerated this study had some limitations including small sample size and lack of randomised control. The efficacy of

everolimus was next investigated in advanced HCC patients who did not respond to sorafenib. In a phase III, randomised, double-blind study (EVOLVE-1, NCT01035229) everolimus did not show improvement in OS (7.6 months with everolimus, 7.3 months with placebo). In a separate phase II study (NCT01005199), patients with advanced HCC were compared to those administered sorafenib alone (800 mg) or with everolimus (5 mg) [38]. The results were not encouraging and combination of sorafenib with everolimus did not improve efficacy compared to sorafenib alone with median PFS (6.6 months *versus* 5.7 months), TTP (7.6 months *versus* 6.3 months), and OS (10 months *versus* 12 months) were similar in the Sorafenib alone group *versus* sorafenib + everolimus, respectively. However, loss of tuberous sclerosis complex 2 (TSC2) in HCC has been reported to be predictive of response to everolimus in HCC patients [39]. Immuohistochemical analysis of HCC samples collected in the EVOLVE-1 clinical trial (NCT01035229) had no detection of TSC2 and longer OS than compared to placebo. A larger study is needed to validate the potential of everolimus before it can be used to stratify HCC patients for response to everolimus.

Another mTOR inhibitor, temsirolimus (taken intravenously) has not improved survival either alone or in combination with either sorafenib [40] or bevacizumab [41]. In a recently concluded phase III study (SILVER, NCT00355862), another mTOR inhibitor, sirolimus, did not improve recurrence-free survival (RFS) or OS beyond 5 years in Ltx recipients with HCC but it did improve RFS and OS within 3–5 years. This may suggest the potential use of sirolimus for selection of immunosuppression in LTx recipients with HCC [42].
