MTOR and cancer: Results from a recent clinical trial have shown that low-dose sirolimus (an mTOR inhibitor) can significantly reduce overgrowth of affected areas.18 Drugs known to target the Mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinases (ERK) pathway (also known as the Ras-Raf-MEK-ERK pathway) pathway are already available and being used in cancer therapy.19 These could represent a new treatment for selected patients with mosaic RASopathies.16