MTOR and neoplasm: Inhibition of tumor proliferation, as reflected by decreased Ki67-positive tumor cells, was more prominent with everolimus plus letrozole compared with letrozole alone (mean reduction at day 15 relative to baseline 90.7% in everolimus group vs. 74.8% in placebo group; p = 0.0002), and inhibition of mTOR activity (decreased pS6K levels) was observed in patients treated with the combination [58].