Aims Despite considerable interest in the PI3K/AKT/mTOR pathway in breast carcinomas (BC), published data reports contradictory results regarding the association of phosphorylated mammalian target of Rapamycin (p-mTOR) expression with clinico-pathological features and prognosis in BC. Here, we evaluate the main clinico-pathological associations with p-mTOR expression in BC, with focus on the different molecular subtypes.

Methods In this retrospective study, 331 BC patients were included in final analysis. Outcome measures included disease-free survival (DFS) and overall survival (OS) times. Baseline data and outcome measures were compared between immunohistochemical p-mTOR expressing and non-expressing BCs. Subgroup analysis was performed to assess the effect of p-mTOR expression in the outcome for each BC molecular subtype.

Results 43.8% of the tumours were positive for p-mTOR, with a significant correlation between p-mTOR expression with smaller (<2 cm) (p=0.021) and lower-grade tumours (p<0.001). Expression of p-mTOR was also associated with longer DFS (HR of 0.32, p<0.001) and OS (HR of 0.20, p<0.001). In a multivariable analysis, the HR remained significant with minimal change (HR=0.26, p=0.002 for OS; HR=0.40, p=0.002 for DFS). In subgroup analysis, luminal p-mTOR-expressing tumours demonstrated longer DFS and OS (HR 0.33, p=0.003; HR 0.20, p=0.003, respectively) independently of size, grade, lymph node status and Her-2 overexpression.

Conclusions p-mTOR expression is associated with smaller, lower-grade and with luminal BC. In multivariable analysis, p-mTOR expression was associated with longer DFS and OS, independently of the size, grade and lymph node status, especially in luminal BCs.